Screenings are tests that look for diseases before you have symptoms. Screening tests can find diseases early, when they're easier to treat. You can get some screenings in your doctor's office. Others need special equipment, so you may need to go to a different office or clinic.

Some conditions that doctors commonly screen for include

• Breast cancer and cervical cancer in women
• Colorectal cancer
• Diabetes
• High blood pressure
• High cholesterol
• Osteoporosis
• Overweight and obesity
• Prostate cancer in men

Which tests you need depends on your age, your sex, your family history, and whether you have risk factors for certain diseases. After a screening test, ask when you will get the results and whom to talk to about them.

Risks are all around us. A nearby sneeze may raise your risk for catching the flu. Obesity boosts the odds you’ll get diabetes. Smoking increases your risk for many cancers. And if you pay attention to news headlines, you may worry that you’re at risk for food poisoning, Zika infection, shark attacks, and more. How can you know which health risks apply to you?

Health risks can sometimes be confusing, but they’re important to understand. Knowing the risks you and your family may face can help you find ways to avoid health problems. It can also keep you from fretting over unlikely threats. Knowing the risks and benefits of a medical treatment can help you and your doctor make informed decisions.

“Understanding health risks is key to making your own health care decisions,” says Dr. William Elwood, a psychologist and behavioral scientist at NIH. “It gives you perspective on potential harms and benefits, so you can make smart choices based on facts and not fears.”

A health risk is the chance or likelihood that something will harm or otherwise affect your health. Risk doesn’t mean that something bad will definitely happen. It’s just a possibility. Several characteristics, called risk factors, affect whether your health risks are high or low.

Your personal health risk factors include your age, sex, family health history, lifestyle, and more. Some risks factors can’t be changed, such as your genes or ethnicity. Others are within your control, like your diet, physical activity, and whether you wear a seatbelt.

When you see health statistics, consider the types of people being described. If they’re not similar to you, or if the category is very broad, then your risks may be different. A general statement like “More than half of Americans over age 45 will develop heart disease at some point” is based on statistical averages across the entire U.S. population. If you’re younger than 45, your heart disease risk will generally be much lower. The more risk factors you have—such as smoking, high blood pressure, or diabetes—the greater your risk. Exercise and a healthy diet, on the other hand, can make your chance of developing heart disease lower than for most other people.

“In many ways, our perception of risk is irrational,” says Elwood. “We sometimes worry over something that’s extremely unlikely, like Ebola in the U.S. And we ignore steps we can take to prevent what’s much more likely to harm us, like heart disease or colon cancer.”

Talking about health risks can seem intimidating. Even doctors sometimes have trouble with risk concepts. That’s why NIH supports research to improve how medical staff and others communicate health risks and prevention strategies to patients and the public.

“Math in general is hard for a lot of people. Yet math is often hidden in everyday activities that affect our health,” says Dr. Russell Rothman, a physician and scientist at Vanderbilt University in Nashville. Rothman’s research focuses on helping people understand and work with numbers, so they can reduce their risks for diabetes and excess weight, including childhood obesity.

Studies show that the way we hear and understand health statistics can be influenced by how the numbers are described, or how they’re “framed.” Different descriptions can affect how clear the information is and also what emotions it stirs. For example, the statement: “More than 20% of Americans will eventually die of cancer” might sound less scary from a different perspective: “Nearly 80% of Americans will not die of cancer.” The same information might seem clearer described as a ratio: “More than 1 in 5 Americans will eventually die of cancer.” Research shows that pictures or diagrams are often the most understandable—for instance, showing 5 human figures with 1 in a different color.

To understand the potential risks or benefits of a medical treatment or behavior change, it helps to focus on a math concept called “absolute risk.” Absolute risk is the chance of something happening, such as a health problem that might arise over a period of time. For example, a disease might affect 2 in 100 middle-aged men over their lifetimes. If a certain drug lowers their risk for the disease to 1 in 100, the drug has reduced their absolute risk by 1 person in 100, or 1%. Another way to think of it is that you’d need to treat 100 people with this medicine to prevent just 1 additional person from getting the disease.

Often, however, you might hear numbers that use a related concept called “relative risk.” Relative risk compares the absolute risks of one group to another. In the example above, you could also say that the drug reduced the risk of disease by 50%, since 1 is half of 2. Looking at relative risk alone, you may mistakenly think that the drug is highly effective.

“Many times, the relative risk sounds much greater than the absolute risk, which can be confusing,” Rothman explains. When you hear numbers about risk, it’s best to focus on the absolute risk.

Health risks can be especially hard to grasp when emotions run high, such as when people are faced with a serious illness. One recent NIH-funded study found that people with advanced cancer tended to expect better outcomes and longer survival times from treatment than their doctors did. Most patients didn’t realize that their outlook differed from their doctors. Such misunderstandings might affect whether patients choose to undergo harsh treatments.

“Communication is a 2-way street,” says the study’s lead researcher, Dr. Ronald M. Epstein of the University of Rochester Medical Center in New York. “For effective discussions to occur, doctors must provide encouragement and answers. And patients have to ask important questions.” Epstein and colleagues are developing methods to help doctors and patients have realistic discussions about topics such as emotions, treatment choices, and likely outcomes.

“We’ve shown it’s possible to improve the conversations. It helps if patients come prepared with 3 or 4 big-picture questions to ask their doctors,” Epstein says. For people with advanced cancer, questions might include: How will treatment affect my quality of life? What’s the average survival time for this type of cancer?

“It can feel scary to ask those kinds of questions. Sometimes you don’t really want to know the answers, or you have mixed feelings,” Epstein says. “Doctors can help by opening the door to conversation. They can say, ‘Tell me what’s on your mind. Do you have any questions?’” Such open conversations can help patients and their families make more informed health decisions.

Start by talking with your doctor about your health risks. Ask how you can reduce your risks. And look to trustworthy websites—like NIH’s health.nih.gov—for reliable health information.

Asking Your Doctor About Health Risks

• What are my personal health risks? Are these risk over my lifetime or over a shorter period?
• What steps can I take to reduce my health risks? (such as through exercise or a healthy diet)
• What are my options? (for treatments, screening tests, or making healthy changes)
• What will the results of this test or therapy tell us about my risks?
• What are possible benefits and side effects? What are the chances these might affect me?

It seems like a new health risk is in the news every day. How do you know which risks are worth worrying about?

A health risk is something that increases your chance of developing a disease. For example, getting too much sun on your skin may put you at higher risk for skin cancer. That doesn’t mean that you will definitely get skin cancer. You can take steps to lower your risk by protecting your skin from sun exposure.

When you hear about a health risk, ask yourself some basic questions to decide what you should do. Who does this health news affect? Are they people like you? Are they your age? Do they live in your area? How certain is this risk? What steps can you take to protect yourself?

You have the power to change many factors that put your health at risk. You can protect your skin from the sun. You can choose to eat healthy food and be physically active. However, you can’t change all the things that affect your health risks. You can’t change your age. You can’t change a family history of an inherited disease.

Ask your doctor about the most important health risks for you. Write down any questions before your visit, and speak up if you don’t understand something.

Knowing and acting on your family health history can be an important part of staying healthy. Family health history can help your doctor decide what screening tests and other interventions you need and when. For example, if you have a parent, sibling, or child with breast cancer, your doctor might recommend that you start mammography screening earlier. Your doctor also might refer you for cancer genetic counseling, especially if your relative was diagnosed before age 50.

Take the time to collect your family health history information from your family members. It might not be easy–your family members might not be used to talking about their diseases or might not want to talk. But starting the conversation is important. Remember, you’re asking not just for your own health, but for the health of everyone in your family.

If you have a medical condition, such as cancer, heart disease, or diabetes, be sure to let your family members know about your diagnosis. If you have had genetic testing done, share your results with your family members. If you are one of the older members of your family, you may know more about diseases and health conditions in your family, especially in relatives who are no longer living. Be sure to share this information with your younger relatives so that you may all benefit from knowing this family health history information.

Are you ready to collect your family health history but don’t know where to start? Here’s how!

Family Health History Checklist: Adults

• Talk to your family. Write down the names of blood relatives you need to include in your history. The most important relatives to include in your family health history are your parents, brothers and sisters, and your children. Next, you may want to talk to grandparents, uncles and aunts, nieces and nephews, and half-brothers and half-sisters.
• Ask questions. To find out about your risk for chronic diseases, ask your relatives about which of these diseases they have had and when they were diagnosed. Questions can include
  • Do you have any chronic diseases, such as heart disease or diabetes, or health conditions such as high blood pressure or high cholesterol?
  • Have you had any other serious diseases, such as cancer or stroke?
  • How old were you when each of these diseases and health conditions was diagnosed?
  • What is our family’s ancestry – from what countries did our ancestors come to the United States?
  • For relatives who have died, be sure to ask about cause and age of death.
• Record the information. Write this information down, and be sure to update it from time to time.
• Share family health history information with your doctor and other family members. Your family health history can give you an idea of your risk for chronic diseases like cancer, heart disease and diabetes, but it is not the only factor to consider. If you are concerned about diseases that are common in your family, talk with your doctor at your next visit. A doctor can evaluate all of the factors that may affect your risk of some diseases, including family health history, and can recommend ways to reduce that risk.
• Act on your family health history. Having a family health history of a disease does not mean that you or your family members will definitely get that disease. It is important that you talk with your doctor about steps that you can take to lower your chances of getting the disease. You have already taken the first step by learning about your family health history!

Blood courses through your body with every heartbeat. It carries life-giving oxygen to every organ. Blood also helps remove the waste products your body makes. Because it flows to and from every part of the body, blood can provide an important window into what’s happening under the skin.

“So many biochemical compounds get absorbed from the tissues of the body into the blood. This makes the blood a really good place to look for hints of disease,” says Dr. Lori Minasian, who helps oversee cancer prevention research at NIH.

Blood tests can help your health care provider diagnose diseases. They can also help them choose the best treatments for many health conditions. Commonly used blood tests look for compounds that signal an increased risk of heart disease. Other tests help diagnose diabetes, vitamin deficiencies, and many types of infections.

Blood tests have been helpful for preventing some common, dangerous health events, like heart attack and stroke. NIH-funded researchers are working to expand the number of health conditions that can be detected with a simple blood test. These include cancer, dementia , and other deadly diseases.

Tracking Cancer

Like normal cells in the body, cancer cells also come into regular contact with blood. This means that substances from tumors, like pieces of genes or even whole cancer cells, can get into the bloodstream.

Researchers have developed tests to look for such substances in the blood. These are called liquid biopsies. These tests are already used for some types of cancer to monitor whether a tumor comes back after treatment, Minasian says. Scientists are also looking at whether these tests can identify which tumors may need more aggressive treatment to prevent them from returning.

Blood tests might one day be used for cancer screening, too. Screening tests aim to catch cancer early—before symptoms develop. Cancers found early are often easier to treat. This can save lives.

Some cancer screening tests are already available through your doctor. These include mammograms for breast cancer and colonoscopy for colorectal cancer. But neither are as simple to do as a blood test.

Many types of cancer still don’t have screening tests available. More than half of cancer deaths are from cancers that don’t have screening tests yet. These include deadly cancers like ovarian cancer and pancreatic cancer.

“The idea that, with a single blood test, you could screen for many deadly cancer types, has huge potential,” says Minasian.

The usefulness of blood tests for cancer screening is still in the early research stages. Right now, there’s limited evidence for any benefits. Despite this, blood tests for cancer screening are marketed directly to consumers. People should be very careful about using these tests right now, Minasian cautions.

“There is not enough data to understand the full risks and benefits of using these blood tests for cancer screening,” she says. “The results could lead to anxiety or may provide a sense of false reassurance.”

If you’re concerned about your cancer risk, talk with a health care provider. They can help you stay up to date with proven screening tests.

Detecting Alzheimer’s Disease

Like your body, your brain is full of blood vessels. So substances from injured brain cells can also enter your blood.

For decades, researchers have been trying to develop blood tests to help diagnose and better treat mental health conditions, explains Dr. John Hsiao, a psychiatrist at NIH. But, this has proven difficult.

Blood tests to determine whether someone is at risk for dementias are showing promise, Hsiao says. The proteins that damage brain cells in these conditions are now well understood. This means they can be measured.

The most common cause of dementia in older adults is Alzheimer’s disease. Measuring Alzheimer’s disease proteins currently requires a brain scan or collecting spinal fluid. These tests can be costly and aren’t available in every community.

“But these abnormal proteins that build up in the brain also show up in the blood,” says Dr. Reisa Sperling, a neurologist at Harvard Medical School. Blood tests for Alzheimer’s have the potential to be “cheap and easy,” Hsiao adds.

Recent studies have shown that blood tests can detect early signs of Alzheimer’s disease in the brain. So researchers are looking at whether they can use them to find and treat people with the disease early. They hope this could help prevent or slow the loss of brain cells.

“Studies so far suggest that our best chance at being able to delay the memory loss and other symptoms of Alzheimer’s disease would be to treat very early,” Sperling says. But she does not recommend people without symptoms get blood tests done outside of studies just yet.

Some blood tests that claim to detect Alzheimer’s disease are being advertised to the public. But they are not yet FDA approved. Sperling warns that some of these tests may not be as accurate as those being used by researchers.

If you’re concerned about your risk for dementia, Sperling recommends joining a clinical study. “There are great research trials for people to go into, and they will use the best blood tests available,” she says.

Researchers are also trying to develop blood tests to detect other causes of dementia and brain conditions like Parkinson’s disease. “These tests have the potential to really change how we diagnose and understand these conditions,” Hsiao says.

Stay Up To Date

It may be a while before a blood draw at your local clinic can find diseases like cancer or dementia. But keeping up with current blood tests can help you get early treatment for other potentially life-threatening problems.

What Blood Tests Do I Need?

Depending on your age and other factors, your health care provider may order tests that measure:

• Blood glucose (sugar): To help diagnose diabetes or see whether you’re at risk for diabetes.
• Blood lipids (fats): To assess your risk for heart disease and related conditions. These tests measure levels of lipids called cholesterol and triglycerides.
• Blood cell counts: To help diagnose many diseases, including infections, cancer, and bleeding disorders. These tests measure the types of cells that carry oxygen and fight diseases.
• Organ function: To make sure organs like your liver, kidneys, and heart are working properly.
• Specific blood-borne diseases: To look for diseases like HIV and hepatitis C, which may not cause symptoms until after they’ve started to damage the body.
• Vitamin deficiencies: To measure levels of vitamins in the body. These aren’t usually recommended for healthy people. But if you have symptoms of some health conditions, your doctor may order tests to look for low levels of some vitamins.

About Cancer Screening

What are cancer screening tests?

Cancer screening tests are used to check for cancer or signs of cancer risk before a person has symptoms. There are two kinds of benefits from cancer screening tests: detection of abnormal cells that can be removed or treated before they become cancer (precancers), and detection of cancer at an earlier stage when it may be more treatable, leading to improved survival.

Cancer screening is not a stand-alone test. The success of a cancer screening test depends on more than just how well the test works. It also depends on the accuracy and affordability of the test, on the diagnostic workup needed after initial testing, and on effective cancer care delivery.

What kind of tests are used to screen for cancer?

Tests to detect cancer or cancer risk come in many forms:

• Physical exams to check general signs of health. These exams can uncover visible signs of disease, such as lumps, abnormal moles, or enlarged organs.
• Imaging procedures, which take pictures of areas inside the body.
  • A mammogram is a screening test for breast cancer. This test is an x-ray picture of the breast. Mammography has been shown to decrease the risk of dying from breast cancer by detecting it earlier when it is usually easier to treat.
  • Low-dose computed tomography (CT) is used to screen for lung cancer. It has been shown to decrease the risk of dying from lung cancer in heavy smokers. The procedure makes a series of detailed pictures of the lungs using a type of x-ray machine.
• Direct observation tests, which involve visual examination of tissue for abnormal growths. A colonoscopy is a screening test for colorectal cancer. In this test, the rectum and colon are examined using a flexible lighted tube with a lens for viewing.
• Laboratory tests, which analyze samples of tissue, blood, urine, or other substances in the body. For example, health care professionals take a sample of cervical cells to screen for cervical cancer with a Pap test and to check for infection with human papillomavirus.

Additionally, standard screening methods for colon and cervical cancers can detect precancers that can be removed (for example, polyps), and thus prevent the development of a cancer in addition to detecting cancer early when it may be easier to treat successfully.

Does a positive cancer screening test mean I have cancer?

No. A screening test alone cannot diagnose cancer. A cancer screening test identifies something abnormal, and then more tests must be done to determine whether a person has cancer and what type. These are called diagnostic tests.

For example, a screening mammogram may find a change in breast tissue. This change may be a cancer or a precancer or something else. More tests need to be done to find out what that tissue change means and whether it requires treatment or if it is a false-positive result. These tests may include a biopsy, in which cells or tissues are removed by a needle or during a surgical procedure so a pathologist can check them under a microscope for signs of cancer.

Does a negative cancer screening test mean I do not have cancer?

No. A screening test can miss the presence of cancer, leading to a false-negative test result. For example, mammograms may appear normal even though breast cancer is present. Overall, screening mammograms miss about 20% of breast cancers that are present at the time of screening.

About Multi-Cancer Detection Tests

What are multi-cancer detection (MCD) tests?

Multi-cancer detection (MCD) tests, also referred to as MCD assays or liquid biopsy tests, measure biological substances that cancer cells may shed in blood and other body fluids – such as circulating tumor cells, tumor DNA, and other analytes – that may suggest the presence of cancer. An assay is a laboratory test to find and measure the amount of a specific substance in a sample such as a liquid biopsy (tests done on a sample of blood, urine, or other body fluids to look for cancer cells, or other molecular evidence of cancer). The biological signals that MCD assays test for are known as biomarkers or tumor markers.

MCD tests differ from other cancer screening tests in two main ways. First, they use a single blood test instead of x-rays or imaging tests (such as mammography) or other medical procedures (such as colonoscopy). Second, they check for many types of cancer from different organ sites at the same time—including some cancers that existing screening tests do not check for.

As a new tool for cancer screening, MCDs make a prediction about the presence of cancer, not a diagnosis.

Depending upon which biological signals the MCD test measures, it may screen for several different types of cancer.

Current MCD tests in development measure different biological signals in blood plasma, such as:

• Changes in DNA and/or RNA sequences
• Patterns of DNA methylation (a chemical change to DNA which changes how the gene product is expressed)
• Patterns of DNA fragmentation (how the DNA is broken into smaller pieces)
• Levels of protein biomarkers
• Antibodies that a person’s body may develop against components of growing cancer cells.

Research scientists continue to search for new technological approaches that may expand this list to measure even more biological signals (e.g., what a person’s immune cells are actively searching for).

To date, no professional medical societies nor the U.S. Preventive Services Task Force have issued recommendations on the use of MCD tests for cancer screening. Health insurance programs do not routinely cover MCD testing. (See below, "Are there Food and Drug Administration (FDA)-authorized MCD tests available in the United States?")

How are MCDs and MCEDs different?

NCI uses the term “Multi-Cancer Detection (MCD) tests,” while some researchers and businesses prefer “Multi-Cancer Early Detection (MCED) tests.” Both acronyms refer to the same type of assay intended to detect cancer in people with no symptoms of cancer.

How are MCD tests different from genetic tests?

While MCD tests analyze molecules released by tumor cells, genetic tests for cancer risk look for specific inherited patterns in a person’s genes, including healthy cells. Genetic variants can have harmful, beneficial, neutral (no effect), unknown, or uncertain effects on the risk of developing diseases. Harmful variants in certain genes are known to be associated with an increased risk of developing cancer. These inherited variants are thought to contribute to about 5% to 10% of all cancers.

Genetic tests are usually requested by a person’s genetic counselor, doctor, or other health care professional who has reviewed the individual’s personal and family history. The genetic test options from which a health professional may select include those that look at a single gene and those that look for harmful variants in multiple genes at the same time. Genetic testing is done on a small sample of bodily fluid or tissue—usually blood, but sometimes saliva, cells from inside the cheek, or skin cells. The sample is then sent to a laboratory that specializes in genetic testing. The laboratory returns the test results to the doctor or genetic counselor who requested the test.

Are there Food and Drug Administration (FDA)-authorized MCD tests available in the United States?

No. The FDA authorizes devices and tests differently from how it approved medicines. No MCD tests have been authorized by the FDA. However, some companies are offering the tests to physicians and consumers as laboratory developed tests (LDTs). LDTs are tests that are designed, manufactured, and used within a single laboratory. Laboratories offering LDTs are required to show that they measure what they say they can measure. The federal regulation of LDTs does not require evidence that they provide a clinical benefit to patients, such as diagnosing cancer early.

A few MCD tests have received a Breakthrough Device Designation from the FDA, but this does not mean they have gone through the FDA’s rigorous premarket review process.

What MCD tests are available to the public in the United States?

This is a rapidly evolving emerging technology. There is no comprehensive centralized listing of MCD tests available to the public.

There are some MCD tests available to the public as laboratory developed tests (LTDs). However, no MCD tests have been authorized by the FDA. LTDs are regulated under the Clinical Laboratory Improvement Amendments of 1988 (CLIA). The federal regulation of LDTs under CLIA does not require evidence that they provide a clinical benefit to patients, such as diagnosing cancer early. (See above, “Are there FDA-authorized MCD tests available in the United States?”)

We do not know if using the current MCD tests available to the public to detect possible cancers is more likely to cause harm than benefit. Randomized clinical trials are needed to assess the risk/benefit ratio of MCDs.

Do health insurance plans pay for MCD tests?

No. Currently, no MCD tests are recommended for reimbursement by the Centers for Medicare & Medicaid Services. Health insurance plans typically will not pay for MCD tests. Most people will have to pay out-of-pocket for the tests, and some people may also have to pay for the follow-up diagnostic procedures out-of-pocket. The cost for MCD tests varies but could cost around $900. There is little known about whether the cost of a diagnostic workup for a positive MCD result would be covered by insurance.

What kinds of cancers can each MCD test potentially find?

Most MCD tests measure different biological signals that may be shed by cancer cells. Depending on what is measured, the cancers that may be detected will vary. Currently, no MCD tests screen for every type of cancer. Tests typically include cancers for which effective screening is already available, such as colorectal cancer and breast cancer, as well as other cancers for which screening is not available. Some MCD tests include highly lethal cancers such as ovarian and pancreatic cancer. One MCD test may screen for colorectal cancer, bladder cancer, and prostate cancer, while another may screen for a different group of cancer types. To date, each MCD test under development looks for a different group of cancers.

Does a positive result on an MCD test mean that a person has cancer?

No. A positive result on an MCD test is just a signal that a person might have cancer. If a person gets a positive MCD result, more tests will be needed (which may include invasive tests and/or biopsies) to confirm a diagnosis of cancer. We do not know if MCD tests will only find cancers that will require treatment or may also identify slow-growing cancers that might never affect a person’s health.

Will an MCD test say what type of cancer a person has?

No. Some MCD tests indicate the likely organ site of the cancer (e.g., lung). Like other cancer detection tests, the MCD test only provides a signal for a possible cancer.

Additional testing, such as imaging, tissue biopsy, and/or surgery is required to diagnose if someone has cancer and if so, which kind of cancer. The type or sequence of additional testing that should be used following a positive MCD test is not yet known.

How many follow-up tests might be needed if an MCD test is positive for cancer?

How much additional testing a person may need after an MCD test to determine if they have cancer, where that cancer is located, and what to do if those additional tests do not show a cancer, is unknown. In published research about people who had a positive MCD test, more than half the time, no cancer could be found.

In addition, follow-up diagnostic tests needed after a positive MCD result may lead to invasive procedures to check all the possible cancer sites that could be involved. There may be complications from those procedures, time spent away from work and family, and anxiety and uncertainty about the testing process. To date, information is too limited to know how frequently to check on these patients and the extent to which patient anxiety and concern about costs will affect adherence to follow-up testing. (See below, “What are the potential harms of MCD tests?”)

Does a negative MCD test mean that a person does not have cancer?

There is limited data. However, patients have been diagnosed with cancer despite having a negative MCD test. As yet, no MCD tests are so accurate or broad that a negative result means that a person does not have cancer.

For example, a person may have a cancer that a MCD test does not detect. A person may have an early stage cancer that a MCD test screens for, but the cancer is missed by the test.

Each MCD test has a different cut-point for determining what constitutes a negative or positive test result. The cut-point is based on a proprietary algorithm (a set of rules for making a prediction) developed using machine learning or artificial intelligence.

Risks, Benefits, and Needed Research

What are the potential benefits of MCD tests for cancer screening?

It is not known whether, and to what extent, the benefits of screening with MCD tests will outweigh the harms for the population in which these tests would be used. In at least one study, half the patients who had a positive MCD test went through diagnostic testing with no cancer detected at one year.

Understanding the benefits and harms of MCD-based screening requires a randomized controlled trial. Potential benefits of MCD screening might include:

• Screening at organ sites currently without a screening test. MCD tests may potentially detect cancers at organ sites where currently no screening is available, and perhaps save lives.
• Earlier detection. MCD tests may potentially detect cancers that are hard to identify when those cancers are in an early stage. Finding cancer at an earlier stage may improve the chance of cure or allow for less invasive treatments.
• Screening for multiple cancers at the same time. MCD tests can potentially identify cancers from many different organ sites with only a single test.
• Less invasive procedures. Most MCD tests rely on a blood draw, which may be more acceptable to patients than other forms of cancer screening tests.

What are the potential harms of MCD tests?

The potential harms of MCDs include:

• Negative results. Participation in MCD testing may provide a false sense of confidence that leads people to skip standard-of-care screening, such as regular mammograms.
• False-negative results. An MCD test may report a negative result when the person has a cancer. This could lead to a delay in cancer treatment if the MCD results provide a false sense of confidence that leads a person to ignore symptoms.
• False-positive results. An MCD test may report a positive result, but further diagnostic procedures do not find a cancer.
• Overdiagnosis and overtreatment. Like other screening tests, MCD tests may not be able to tell the difference between cancers that grow slowly and may never require treatment from those that lead to illness or death.
• Early detection of some types of cancer may not make a difference in a person’s treatment options, survival, or chance of dying from the disease.
• Uncertainty and potential harms from procedures needed to diagnose the cancer. Some companies producing MCD tests provide a list of potential organ sites for cancer to support a health care provider in starting a diagnostic workup. However, a positive MCD test could potentially result in multiple follow-up tests, leading to a prolonged process to find out if any cancer is present. This prolonged process can cause patient anxiety, require time, and lead to financial expense. These follow-up procedures each carry their own risks and have the potential to cause physical harm.
• MCD tests may increase medical mistrust if test characteristics and/or results are not adequately explained or appropriately understood by the public.
• MCD tests could make existing health disparities worse. Not all individuals may have access to health care to have follow-up diagnostic/screening tests after a positive MCD result. This unequal access to cancer screening and necessary health services may worsen existing health disparities. Only randomized controlled trials that follow people over time and consider the complex set of factors involved in testing for multiple different kinds of cancers can determine how the potential benefits of MCD tests stack up against potential harms.

Do MCD tests address health disparities?

The impact of MCD-based cancer screening on healthcare disparities is unknown. More research is needed to understand whether MCD tests improve access or worsen health care disparities. Clinical trials to determine the benefits and harms of MCD tests should enroll a broad and diverse range of population groups, so that we can determine whether all communities will benefit or be harmed by these tests.

If MCD tests and follow-up procedures needed to make a diagnosis are not widely available and affordable, inequities for minority, underserved, and vulnerable populations could increase. Plus, a screening test cannot address the availability and affordability of appropriate treatments if a cancer diagnosis is ultimately made.

MCD screening might also help narrow the disparities gap in cancer clinical care by increasing the participation rate with available cancer screening programs through improvement in access to screening of underserved and socioeconomically disadvantaged populations.

What is not yet known about MCD tests?

MCDs have the potential to transform how we think about and implement cancer screening. More than half of cancer deaths involve cancers that have no recommended screening tests, including highly deadly cancers like ovarian and pancreatic cancer. The potential risks and benefits for using emerging technologies such as MCD tests for cancer screening are unknown.

Currently, data indicate that MCD tests are better at detecting later-stage cancer than early stage disease. Therefore, it is critical to determine whether using these tests will reduce deaths due to cancer compared with not using such tests.

There are many unanswered questions about the use of MCD tests to screen for multiple cancers. Other unanswered questions include:

• What kind and how many diagnostic tests will be needed following an MCD test to make a cancer diagnosis?
• What happens if following a positive MCD test, a cancer is not found?
• How many people will receive unnecessary invasive procedures and suffer from various complications of those procedures following positive MCD tests?
• Will people stop standard-of-care screening, such as mammograms and colonoscopies, if they get a negative MCD test?
• Do MCD tests work equally well in all populations?
• Will MCD tests make screening more accessible or increase health disparities?
• Will MCD tests lead to overdiagnosis of slow-growing cancers that would not have caused illness or death?

Despite these unknowns, healthcare professionals and patients are faced with a marketing tsunami of MCD tests in various stages of development. To date, there is not enough information available about MCDs for doctors to adequately inform their patients.

Rigorous clinical trials are needed to determine whether using MCD tests to screen asymptomatic people will reduce cancer deaths without causing substantial harms, such as suffering and anxiety from inconclusive or negative diagnostic workups triggered by a positive result on a MCD test. To date, there are no definitive clinical trials showing that use of MCD tests for cancer screening will reduce overall cancer mortality.

What research and clinical trials are underway to develop MCD tests?

There are several studies in development to evaluate the effectiveness of MCD tests in detecting cancers in individuals without cancer symptoms. The National Health Service in the United Kingdom, for example, is enrolling people to a randomized controlled trial to see whether screening with a MCD test (along with standard screening) reduces the occurrence of late-stage cancers, and possibly death, compared to standard screening alone. Companies that make MCD tests and research groups are continuing to investigate additional approaches to develop new MCD tests.

What research is NCI doing on MCD tests?

The potential of MCD tests is exciting. If found to be useful, these new blood tests could provide the opportunity for less invasive tools for the early detection of cancer. No clinical trials have been conducted to determine whether using these tests to screen for cancer will lower the burden of cancer within populations.

Clinical trials of MCD tests are needed to understand whether their use can save lives. Only a clinical trial that follows many people over time can determine if the potential benefits outweigh the potential harms. Answering this question is an urgent matter; some of these tests are already available to the public, although none have been proven to reduce mortality from cancer.

NCI is working on a broad template for how to conduct a clinical trial with this new type of screening test. A key feature of such a trial is determining the clinical utility of MCD tests by measuring whether the tests result in fewer cancer deaths in the population of screened individuals compared to a control population. There are many MCD tests in development by a variety of companies, all of which will need clinical trials to understand their potential benefit.

NCI is setting up a network of researchers to find the best ways to test MCDs in clinical trials. In June 2022, the NCI Board of Scientific Advisors approved a proposal to create a Cancer Screening Research Network (CSRN), a new network of organizations that includes health care systems, military healthcare and academic institutions, federally qualified health centers, and at least one tribal nation . The CSRN will conduct rigorous, multi-center cancer screening trials and studies with large and diverse populations in a variety of health care settings with the ultimate goal of reducing the number of cancer-related deaths and illnesses.

In 2025, the CSRN will begin enrolling up to 24,000 healthy people aged 45-70 in a Vanguard study to assess the feasibility and finalize the design and logistics for a later, larger study. The Vanguard study will explore the best way to study MCDs and lay the groundwork for future large-scale clinical trials and other studies to assess multiple different technologies for cancer screening.

In addition, NCI is funding the collection of blood samples from patients with cancer and healthy persons to establish a large bank of case-control samples to use in evaluating MCD tests in future studies.

Catching chronic health conditions early—even before you have symptoms—seems like a great idea. That’s what screening tests are designed to do. Some screenings can reduce your risk of dying from the disease. But sometimes, experts say, a test may cause more harm than good. Before you get a test, talk with your doctor about the possible benefits and harms to help you decide what’s best for your health.

Screening tests are given to people who seem healthy to try to find unnoticed problems. They’re done before you have any signs or symptoms of the disease. They come in many forms. Your doctor might take your health history and perform a physical exam to look for signs of health or disease. They can also include lab tests of blood, tissue, or urine samples or imaging procedures that look inside your body.

“I wouldn’t say that all people should just simply get screening tests,” says Dr. Barnett S. Kramer, a cancer prevention expert at NIH. “Patients should be aware of both the potential benefits and the harms when they’re choosing what screening tests to have and how often.”

Teams of experts regularly look at all the evidence about the balance of benefits and harms of different screening tests. They develop guidelines for who should be screened and how often.

Choosing whether you should be screened for a health condition isn’t always easy. Screening suggestions are often based on your age, family health history, and other factors. You might be screened for many conditions, including diabetes, sexually transmitted infections, heart disease, osteoporosis, obesity, depression, pregnancy issues, and cancers.

Every screening test comes with its own risks. Some procedures can cause problems like bleeding or infection. A positive screening test can lead to further tests that come with their own risks.

“Most people who feel healthy are healthy,” says Kramer. “So a negative test to confirm that you’re healthy doesn’t add much new information.” But mistakenly being told that you do or don’t have a disease can be harmful. It’s called a misdiagnosis.

A false negative means that you’re told you don’t have the disease, but you do. This can cause problems if you don’t pay attention to symptoms that appear later on because you think you don’t have the disease. A false positive means that you’re told you may have the disease, but you don’t. This can lead to unnecessary worry and potentially harmful tests and treatments that you don’t need.

Even correctly finding a disease may not improve your health or help you live longer. You may learn you have an untreatable disease long before you would have. Or find a disease that never would have caused a problem. This is called overdiagnosis. Some cancers, for example, never cause symptoms or become life-threatening. But if found by a screening test, it’s likely to be treated. Cancer treatments can have harsh and long-lasting side effects. There’s no way to know if the treatment will help you live longer.

An effective screening test may decrease your chances of dying of the condition. Most have not been shown to lengthen your overall life expectancy, Kramer explains. Their usefulness varies and may depend on your risk factors, age, or treatment options.

If you’re at risk for certain health conditions—because of a family history or lifestyle exposures, like smoking—you may choose to have screenings more regularly. If you’re considering a screening, talk with your health care provider.

Ask Your Doctor About Screening Tests

• What’s my chance of dying of the condition if I do or don’t have the screening?
• What are the harms of the test? How often do they occur?
• How likely are false positive or false negative results?
• What are possible harms of the diagnostic tests if I get a positive screening result?
• What’s the chance of finding a disease that woudn’t have caused a problem?
• How effective are the treatment options?
• Am I healthy enough to take the therapy if you discover a disease?
• What are other ways to decrease my risk of dying of this condition? How effective are they?

You can play an active role in your health care by talking with your doctor or health care provider. Clear and honest communication between you and your physician or health care team can help you both make informed choices about your health. It’s important to be honest and upfront about your symptoms even if you feel embarrassed or shy. Have an open dialogue with your doctor or health care provider— ask questions to make sure you understand your diagnosis, treatment, and recovery.

Here are a few tips that can help you talk to your doctor or health care provider and make the most of your appointment:

• Write down a list of questions and concerns before your appointment.
• Consider bringing a close friend or family member with you.
• Take notes about what the doctor or health care provider say or ask a friend or family member to take notes for you.
• Learn how to access your medical records, so you can keep track of test results, diagnoses, treatments plans, and medications and prepare for your next appointment.
• Ask for the doctor’s or health care provider’s contact information and their preferred method of communication.
• Remember that nurses and pharmacists are also good sources of information.