Cells are sometimes thought of as being the smallest unit of a living organism. The adult human body is made up of about 10 trillion cells. Even the largest cell produced by the body, a fertilized egg, is too small to be seen by the naked eye. Cells come in many different sizes and shapes and perform a myriad of functions. Many cells are attached to other cells to form tissues, such as skin tissue or muscle tissue. Other cells move around the body freely, like white blood cells. Some cells have as their primary function the production of certain substances. Different types of glandular cells, for instance, secrete hormones, enzymes, and mucous. Other cells don't produce substances but have specific functions. Heart muscle cells, for example, pulsate continuously for the duration of their existence, and nerve cells conduct electrical impulses throughout the body. Cells multiply at different rates, too. Hair cells, blood cells, and cells in the intestinal lining reproduce quickly, while nerve cells seldom if ever divide.

Cells in adults normally display tightly controlled patterns of growth. They divide slowly and have definite lifespans. In this way, the number of cells in the body remains roughly the same over time.

Cancerous cells display uncontrolled growth (that is, they start dividing beyond normal limits). The rate of division is faster in some cancers than in others, but in all cancers, the cells never stop dividing: they have infinite lifespans. They invade neighboring tissues, and they may metastasize (spread to distant parts of the body). Generally these cells form a tumor, or mass, although some (like leukemia) do not. Tumors may be benign or malignant.

• Benign tumors don't destroy neighboring tissues, don't spread throughout the body, and stop growing before they become very large. Moles and warts are benign tumors.

• Malignant tumors invade adjacent tissues, metastasize throughout the body, and never stop growing.

Critical to the growth of malignant tumors is angiogenesis, the formation of new blood vessels. Malignant tumors have the ability to produce activator molecules, such as vascular endothelial growth factor. Activator molecules induce the formation of new blood vessels to supply the tumor, allowing for cell reproduction and tumor growth. The branch of medicine that deals with the study, diagnosis, treatment, and prevention of cancer is called oncology.

Metastatic Cancer

Cancer spreads locally by invading neighboring tissues. It can also metastasize (spread to distant parts of the body) by entering the circulatory system or the lymphatic system. This happens when cells break away from the original, or primary, tumor, penetrate into a blood vessel or lymphatic vessel, and travel to another part of the body. Cancer cells don't adhere to one another as well as normal cells, and it's theorized that tumors generate substances that stimulate cancer cells to move.

Metastatic cancers may be found when the primary tumor is found, or they may be found months or even years later.

Spreading: Circulatory System

Almost from the time they first arise, cancerous tumors shed cells into the bloodstream. In fact, it's estimated that a 1-cm tumor sheds more than a million cells into the circulatory system in just 24 hours. Most of these cells are killed by white blood cells or die from damage sustained while traveling in the bloodstream, but some may survive. Sometimes cancer cells stick to platelets to form clumps, giving them some protection. The traveling cancer cells may become stuck in a capillary and adhere to its lining. From there they penetrate into surrounding tissues or organs, where they may generate secondary tumors. Secondary tumors grow in the same way that primary tumors do, and they themselves may start to shed cells and give rise to other metastases.

Spreading: Lymphatic System

Cancer cells may also enter into the lymphatic system. The lymphatic system works in concert with the immune system and has several functions in the body, including combating invasive foreign bodies (like bacteria, fungi, and viruses), filtering lymph, and filtering blood.

Lymphatic vessels form a sort of parallel circulatory system, branching throughout the tissues of the body. Lymph is a clear, colorless liquid found within the lymphatic vessels. It's collected from tissues in all parts of the body as interstitial fluid, and then travels to at least one lymph node for filtering before returning to the bloodstream via the veins. Lymph nodes are found in the armpits, on either side of the groin, on either side of the neck, and in the abdomen, pelvis, and chest. Lymph nodes filter the lymph fluid as it passes through them.

A cancer cell enters a lymphatic vessel in much the same way it enters a blood vessel. Then it travels in the circulating lymph fluid until it becomes lodged in the small channels inside a lymph node, where it begins to grow into a secondary cancer.

Where Cancer Spreads

The most common places for cancer to spread via the circulatory system are the lungs, liver, brain, and bones. All the blood in the body passes through the lungs, so they are a common place to find secondary cancers. Blood from the organs of the digestive system goes through the liver before returning to the heart and then the lungs. Consequently, cancers of the digestive system often spread to the liver. Prostate cancer frequently metastasizes to the bones, for reasons which aren't yet entirely understood.

Cancer cells may spread to lymph nodes near the primary tumor (termed nodal involvement or regional disease). This is not considered metastasis, but it is a sign that the cancer is advancing. The lymph nodes draining an organ are likely to contain cancer cells, so during cancer surgery a surgeon will normally remove the main lymph nodes closest to the tumor. Travel through lymphatic vessels is the most common way for cancer to spread initially.

How Cancer Is Named

Wherever a cancer spreads, the cancer cells are still clones of the original abnormal cell. Because of this, cancers are named after the place where they first arose. For example, breast cancer that has spread to the lungs is termed metastatic breast cancer, not lung cancer. A pathologist doing a biopsy of a tumor can usually see if the type of cell in the tissue sample is normally found in the part of the body from which it was taken. In this way, it can be determined if the tumor is primary or secondary.

There are over 100 different types of cancer. They are diagnosed according to a number of factors, for instance, the location of the cancer and its appearance under a microscope. However, all cancers can be classified into four main categories: carcinoma, leukemia, lymphoma and myeloma, and sarcoma.

Carcinoma

About 80% of all cancer cases are carcinomas. Carcinomas are cancers of the epithelial cells, that is, the cells that line or cover the body's organs, produce hormones, and make up glands. Carcinomas may develop in the reproductive organs, lungs, mucous membranes, and breasts, as well as the liver, prostate, pancreas, thyroid, and ovaries. Carcinomas tend to occur more often in older than in younger people.

Most carcinomas are either glandular (adenocarcinoma) or squamous (squamous cell carcinoma).

• Adenocarcinomas are cancers that develop in the lining or inner surface of an organ. Most stomach, pancreatic, prostate, and breast cancers are adenocarcinomas.
• Squamous cell carcinomas are common skin cancers.

Sarcoma

Sarcomas are cancers of the mesodermal (connective tissue) cells, the cells that form muscle, cartilage, fibrous tissue, bone, and fat. Examples of sarcomas are osteosarcoma (bone cancer) and leiomyosarcoma (cancer of the smooth muscle that is found in the wall of digestive organs). Sarcomas occur more often in younger than in older people. They are rare, accounting for only 1% of all cases of cancer.

Sarcomas are divided into bone and soft-tissue tumors. Bone tumors are much more common. Tumors may have the characteristics of muscle (myosarcoma), bone (osteosarcoma), cartilage (chondrosarcoma), or blood vessels (angiosarcoma).

Lymphoma and Myeloma

Lymphoma and myeloma are cancers that originate in the cells of the immune system.

Lymphomas are cancers of the lymphatic system. They usually start in the lymph nodes or in lymphoid tissues of other organs, such as the lungs, spleen, and skin. There are over 20 types of lymphoma, but they are generally classified into two types: Hodgkin's disease and non-Hodgkin's lymphoma.

• Hodgkin's disease results in enlargement of the lymph nodes and spleen and generally has a high cure rate.
• Non-Hodgkin's disease is classified according to the morphology of the cells and whether the tumors are diffuse or nodular. The nodular form of the disease is less aggressive than the diffuse type. Diffuse large-cell lymphomas tend to progress rapidly and may spread to the liver, kidneys, lungs, and even the brain.

Myelomas are cancers that occur in bone marrow. Myeloma can affect any bone that contains marrow, including the skull, ribs, pelvis, shoulder blades, and vertebrae. In myeloma, abnormal plasma cells populate the bone marrow throughout the body. These cells produce a protein that replaces the normal antibodies in the blood, reducing the body's ability to ward off infection. Myeloma can damage the kidneys or cause complete kidney failure, and it causes the bones to weaken, leading to chronic fracturing. The disease usually occurs during middle age or later. It is progressive and considered incurable.

Leukemia

Leukemias are cancers of the blood or blood-forming organs. Leukemia causes the uncontrolled growth of abnormal cells in the bone marrow, crowding out normal cells and not allowing enough space in the bone marrow for normal blood production. The lack of white blood cells increases the risk of infection, the lack of red blood cells causes anemia and fatigue, and the lack of platelets increases the risk of bleeding in the patient.

Leukemias are categorized as either acute or chronic and as either myelogenous (from bone marrow) or lymphocytic (involving lymphocytes). Acute lymphocytic leukemia, the most common form in children, once killed more than 90% of those who developed it within 6 months. However, thanks to new drug therapies, most acute lymphocytic patients now achieve complete remission. Chronic leukemias, which have a more gradual onset and a more protracted course, arise more frequently in adults.

Cancer staging, that is, determining the extent and spread of cancer in the body, is used by doctors to plan treatment and to arrive at a prognosis (estimate of future course and outcome) for the disease.

How Staging Is Done

Staging involves gathering different types of information to get as clear a picture as possible of the cancer and how far it has progressed. Physical exams, imaging tests (such as MRIs, CT scans, X-rays, PET scans, and PET/CT scans) may all be used. A biopsy is needed to confirm a diagnosis of cancer, but it can also help to stage the disease.

Types of Staging

There are different types of staging:

• Clinical staging is done when the cancer is diagnosed and before treatment. It is based on the physical exam, imaging tests, and, possibly, biopsy. Blood tests may be used for some cancers. This is the stage at which a course of treatment is decided upon.
• Pathologic staging is performed after the patient has had surgery to remove the cancer or to determine the extent of cancer in the body. The surgery may show, for instance, that there is more cancer in the body than had been previously thought, and this will affect prognosis.
• Restaging may be performed to determine the extent of the cancer if it recurs after treatment.

Staging Systems: The TNM System For most cancers, staging is done using the TNM system, developed by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC).

In the TNM system:

• T = extent of the primary tumor
• N = extent of spread to lymph nodes
• M = presence of metastasis

In the T category:

• TX = Primary tumor cannot be evaluated
• T0 = No evidence of primary tumor
• Tis = Carcinoma in situ (early cancer that has not spread to neighboring tissue)
• T1-T4 = Size and/or extent of the primary tumor

In the N category:

• NX = Regional lymph nodes cannot be evaluated
• NO = No regional lymph node involvement (no cancer found in the lymph nodes)
• N1-N3 = Involvement of regional lymph nodes (number and/or extent of spread)

In the M category:

• MX = Distant metastasis cannot be evaluated
• MO = No distant metastasis (cancer has not spread to other parts of the body)
• M1 = Distant metastasis (cancer has spread to distant parts of the body)

However, each type of cancer has its own classification system, so these designations don't mean the same thing for every kind of cancer.

Stage Grouping Once T, N, and M are determined, they are combined, and an overall stage of 0-IV is assigned.

• Stage 0: Carcinoma in situ (early cancer that is present only in the layer of cells in which it began)
• Stage I, Stage II, and Stage III: Higher numbers indicate more extensive disease, ie, greater tumor size, and/or spread of the cancer to nearby lymph nodes, and/or organs adjacent to the primary tumor
• Stage IV: The cancer has spread to another organ

Sometimes these stages are subdivided (eg, IIIA and IIIB).

Criteria for stages differ for different types of cancer. For example, bladder cancer T3N0M0 would be termed Stage III; however, colon cancer T3N0M0 would be Stage II.

Summary Staging Many cancer registries, such as the National Cancer Institute's Surveillance, Epidemiology, and End Results Program (SEER), use summary staging for all types of cancer. Summary staging groups cancer cases into five main categories:

• In situ: Early cancer that is present only in the layer of cells in which it began
• Localized: Cancer that is limited to the organ in which it began, without evidence of spread -Regional: Cancer that has spread beyond the primary site to nearby lymph nodes or organs and tissues
• Distant: Cancer that has spread from the primary site to distant organs or distant lymph nodes
• Unknown: Cases for which there is not enough information to indicate a stage

Other Staging Systems

Leukemia and cancers of the central nervous system are not staged using the TNM system. In leukemia, the cancer is assumed to have spread throughout the body via the circulatory system. Cancers of the central nervous system (the brain and spinal cord) can disrupt vital functions even before they spread, so their progress is not judged in the same way as other cancers. These cancers are classified according to their cell type and grade.

Some physicians still use older staging systems, and certain organizations have developed their own staging systems for specific types of cancer. For instance, the Dukes system is an older staging system for colorectal cancer that is still in use. The International Federation of Gynecologists and Obstetricians (FIGO) has a staging system for cancers of the female reproductive organs.

A Cancer's Stage Doesn't Change

A somewhat difficult concept to grasp is that a cancer's assigned stage doesn't change, even if the cancer progresses or recurs. The cancer is always referred to by the stage it was designated as when it was first diagnosed. So if someone was diagnosed with Stage II colorectal cancer and it metastasized to the liver, it would be called Stage II colorectal cancer with metastasis in the liver. If the colorectal cancer had been treated but then recurred, it would be termed Stage II colorectal cancer with recurrent disease in the liver. It's important to know this, as survival statistics and treatment information are based on the stage when the cancer was first diagnosed.

Another technique that aids doctors in planning treatment and estimating prognosis for the disease is called tumor grading. Tumor grading is a system in which cancer cells are classified according to how abnormal their appearance is under a microscope and how quickly the tumor is likely to grow and spread.

• Histologic grade (differentiation) refers to how much the tumor cells resemble normal cells of the same tissue type.
• Nuclear grade refers to the size and shape of the nucleus in tumor cells and the percentage of tumor cells that are dividing.

How Tumors Are Graded

Pathologists examine the tumor cells under a microscope and usually describe their grade by four degrees of severity: Grades 1, 2, 3, and 4. Grade 1 cells are well differentiated; that is, they resemble normal cells. Grade 1 cells tend to grow and multiply slowly. Grades 3 and 4 tumors are poorly differentiated or undifferentiated (are highly abnormal in appearance) and tend to be more aggressive and spread quickly.

Not all tumors are graded. Tumors that are graded include soft tissue sarcomas, primary brain tumors, lymphomas, and breast and prostate tumors. Different grading systems are used for the types of cancer that are graded. The Gleason system, for example, is used to describe prostate cancer cells; the Bloom-Richardson system is used for breast cancer; and the Fuhrman system is used for kidney cancer.

Scientists have identified numerous risk factors for cancer:

• Tobacco use is the single largest causative factor for cancer, accounting for about 30% of all cancer deaths in developed countries
• Age over 65
• Overweight and obesity
• Inactive lifestyle, lack of physical exercise
• Diet high in fats, particularly saturated fats, and low in fruits, vegetables and fiber. Consumption of preserved meat, red meat, or pickled foods is a risk factor.
• Viruses, including Epstein-Barr virus, hepatitis B or C virus, human papillomaviruses (HPV), and herpesvirus 8
• Bacteria (eg, Helicobacter pylori)
• Parasites (eg, Schistosoma haematobium, human blood fluke)
• Environmental and industrial toxins (eg, benzene, asbestos, tetrachlorethylene, lead, formaldehyde, pesticides, and arsenic)
• Radiation, including UV radiation and ionizing radiation (nuclear, X-ray); the radioactive gas radon - Drugs (eg, estrogen and progestin, diethylstilbestrol [DES], anabolic steroids)
• Immunologic disorders, whether acquired, inherited, or due to immunosuppressants

Environmental Carcinogens

Although certain chemicals found in the workplace and in the environment are known carcinogens, less than 5% of all cancers are currently believed to be due to factors in the environment such as environmental pollution (2%), industrial products (1%), or food additives (1%). However, some research has shown that environmental toxins may cause more cancer than previously thought. Researchers have found that exposure to organochlorides (found in pesticides and plastics) in even small amounts may result in increased risk for certain cancers, especially for young adults and children. For most people, the main source of organocholoride exposure is from diet, primarily through meat and dairy products. Given that a diet high in animal fats and meat is already a known risk factor, it makes sense to lessen consumption of these foods and eat larger amounts of fruits, vegetables, beans, and nuts.

How Cancer Begins

Cancer begins when a cell undergoes a mutation, that is, one or more of its genes is damaged or lost. Mutations can occur when a cell is reproducing, but it's not easy for a cell to become cancerous. About six different mutations have to happen before the cell becomes a cancer cell. And, if a cell carries a mutation, it usually either destroys itself or is recognized as being abnormal by the immune system and killed. This is why cancer usually occurs in older people: there has been more time for exposure to carcinogens and for chance mutations to occur.

Genes at Risk

There are three different types of genes that can have an important part in making a cell turn malignant:

• Oncogenes ("cancer genes") encourage the cell to multiply. Normally, in adults, cells divide only rarely, for instance to replace cells damaged by a wound. If these genes become abnormal, however, they can instruct the cell to multiply without stopping, protect it against programmed cell death, and give it the ability to live in diverse tissues.
• Tumor-suppressor genes tell the cell to stop multiplying. If a tumor-suppressor gene is damaged, the cell won't receive the instruction to stop doubling and will multiply without stopping. This infinite lifespan is one of the hallmarks of a cancer cell. The best-known tumor-suppressor gene is called p53. p53 is damaged or missing in most human cancers.
• DNA repair genes repair damage to the DNA of other cells' genes. If the repair genes themselves are damaged, other mutations aren't repaired and the abnormal cell copies its mutations into its daughter cells.

How Genes Are Damaged

Genes become damaged in several ways:

• Damage due to free radicals produced in the normal process of metabolism
• Exposure to carcinogens, such as radiation, chemicals, tobacco, and infectious agents
• Random errors in DNA replication
• Inherited mutated gene

Genetic Predisposition

People who are said to have a genetic predisposition to certain types of cancer have a greater chance of developing that cancer than other people. This is because they were born with one of the mutations that can lead to a cell becoming cancerous. They may never develop that cancer, because the further mutations that cause the cancer may never take place. But they are at higher risk, because fewer mutations need to take place in their genes for the disease to arise.

The symptoms of cancer depend on the type of cancer, its location, the size of the tumor, and how much it affects nearby organs or tissues. If a cancer has metastasized, symptoms may appear in different parts of the body.

Some cancers may be asymptomatic (have no symptoms at all) or be asymptomatic until the cancer has reached an advanced stage. Pancreatic cancer, for example, may not cause symptoms until the cancerous cells have grown around nearby nerves, causing backache, or around the bile duct, creating jaundice. At that point the cancer is quite advanced.

General Symptoms

The following symptoms can occur with most cancers:

• Chills
• Fever is very common, but occurs most often when cancer has metastasized. It can sometimes be an early symptom of blood cancer (eg, leukemia or lymphoma).
• Fatigue (extreme tiredness that doesn't get better with rest) may be an important symptom as cancer grows. It may happen early, though, in cancers like leukemia, or if the cancer is causing blood loss, which can happen with some colon or stomach cancers.
• Malaise (vague feeling of bodily discomfort)
• Night sweats
• Unexplained weight loss of 10 pounds or more may be the first symptom of cancer.
• Loss of appetite
• Pain generally occurs when cancer has metastasized, but may be an early symptom of bone or testicular cancer. Headache may be a symptom of brain cancer. Back pain can be a symptom of colorectal or ovarian cancer. Cancer is painful because it invades tissues and compresses the nerves.

Symptoms like fever, fatigue, and weight loss can occur for several reasons: because cancer cells use up much of the body's energy supply; because the cancer may release substances that change the way the body metabolizes food, or because the cancer may produce these reactions from the immune system.

Specific Symptoms

The following symptoms are the ones most commonly seen with different forms of cancer:

• Change in bowel habits or bladder function, including long-term constipation, diarrhea, or bloody or narrowed stools may be symptoms of colorectal cancer. Change in bladder habits, pain when urinating, or passing blood may be symptoms of bladder or prostate cancer.
• Sores that do not heal, on the skin, in the mouth, or on the genital organs may be symptoms of skin or oral cancer.
• White patches inside the mouth or white spots on the tongue may be precancerous lesions called leukoplakia, often caused by tobacco use. Leukoplakia can develop into oral cancer.
• Unusual bleeding or discharge can occur in either early or advanced cancer. Bloody sputum can be a symptom of lung cancer, unusual vaginal bleeding can be a sign of cervical cancer, and bloody discharge from the breast can indicate breast cancer.
• Thickening or lump can be an early or late symptom of cancer of the breast, testicle, lymph nodes, and soft tissues of the body.
• Indigestion or trouble swallowing can be symptoms of cancer of the esophagus, throat, or stomach.
• Change in the appearance of a wart, mole, or freckle or any new skin change may be melanoma (skin cancer).
• Nagging cough or hoarseness can be symptoms of lung cancer or cancer of the larynx or thyroid.

How Imaging Is Used

Medical imaging technology has revolutionized the screening, study, and treatment of cancer. Imaging is used before, during, and after cancer treatment:

• Screening. Generally used for people at increased risk of certain types of cancer, screening can help determine if there are abnormal areas present that may be cancerous.
• Diagnosis and staging. Imaging can be used to find out how much cancer is in the body, where it's located, and if it's metastasized. Imaging can also be used as an aid in biopsy to guide the doctors to the tumor.
• Treatment. Imaging can help to guide cancer treatments by exactly determining tumor location, so that treatment can focus on the tumor alone to minimize damage to nearby tissue. Imaging can also show if a treatment is working by showing if a tumor is shrinking, has changed, or is using less of the body's resources.
• Monitoring for recurrence. After treatment, imaging can be used to see if a cancer has recurred or if it has metastasized elsewhere.

Types of Imaging Technology

A number of different types of imaging are used in detecting and treating cancer:

• X-ray imaging is used in cancer screening and diagnosis. Mammograms are a form of X-ray used for screening, and they are also used (along with chest radiographs) to determine if cancer has metastasized to other areas of the chest.
• Ultrasound uses high-frequency sound waves and their echoes to produce a picture of internal organs or masses on a computer screen. The test is painless and does not expose the patient to radiation.
• Magnetic resonance imaging (MRI) scans provide images of soft tissues in the body using radio waves and strong magnets. A computer translates the pattern into a very detailed image of parts of the body. A contrast material is often injected into a vein before the scan to provide clearer images.
• Computerized tomography (CT) scans use multiple X-ray images to produce detailed cross-sectional images of the body. As the patient lies on a table, the CT scanner takes numerous X-rays as it rotates around him or her. Sometimes the patient is injected with a contrast dye the help outline structures of the body. A computer program then combines the images to form detailed cross sections, or slices, of the part of the body being studied. Unlike regular X-rays, CT scans can create detailed images of the body's soft tissues. Spiral CT is a recent advance in CT imaging. It uses a faster machine that rotates around the body continuously, collecting images more quickly and thus lessening the chance that the images will blurred as a result of breathing motion. In addition, the patient receives less radiation with spiral CT, and the cross sections are thinner, producing more detailed pictures.
• Positron emission tomography (PET) scans involve injecting a form of slightly radioactive glucose (known as fluorodeoxyglucose or FDG) into the blood. Cancer cells in the body grow rapidly and absorb large amounts of glucose. The body is then photographed by a special camera to show areas of high glucose concentration.
• PET/CT scans are a recent development. PET/CT scanning machines can perform both a PET and a CT scan at the same time, producing images that reflect both the body's organ function and its structural appearance. The radiologist can compare areas of higher radioactivity on the PET with the appearance of those areas on the CT, improving the ability to detect abnormal areas.
• Single photon emission computerized tomography (SPECT) scans are similar to PET scans. In a SPECT scan, radioactive tracers linked to antibodies (proteins that recognize and stick to tumors) are injected into the patient. If a tumor is present, the antibodies will adhere to it, and the SPECT scan will reveal its presence.

Common Screening Tests

Breast cancer

• Mammography: Women age 40 and older should have a mammogram every year.
• Clinical breast exam (breast exam performed by a medical professional): Women age 20-40 should have one every 3 years. Women 40 and older should have one every year.
• Breast self-exam: Women age 20 and older should perform one each month (considered optional).

Cervical cancer

• Pap test (cells from the cervix and vagina are examined): Women should have a pap test starting 3 years after becoming sexually active or beginning at age 21. A standard pap test should be done each year, or a liquid pap test can be done every 2 years.
• Pelvic exam: Women age 18-40 should have one every 1-3 years. Women age 40 and older should have one every year.

Colorectal cancer

• Colonoscopy (colon is examined from within using a camera attached to a long, thin tube): Men and women 50 and older should have a colonoscopy every 10 years.
• Fecal occult blood test (FOBT): Men and women 50 and older should have one every year.
• Sigmoidoscopy (like a colonoscopy but examines only the lower part of the colon): Men and women 50 and older should have one every 5 years.

Prostate cancer

• Prostate-specific antigen (PSA) test (measures marker that may indicate presence of prostate cancer): Men 50 and older should be offered testing every year.

Skin cancer

• Complete skin examination (doctor checks for signs of skin cancer): Men and women should have one done periodically.

Tumor Markers

A promising development in cancer screening is the use of tumor markers to detect the presence of cancer. Tumor markers are substances produced by tumors or other cells of the body in response to the presence of cancer. They may be found in abnormal amounts in the blood, urine, or tissues of some people with cancer. However, tumor markers alone can't be used to diagnose the disease; they must be used in conjunction with other tests. Sometimes a person with cancer may have normal tumor marker levels, and someone with a different condition may have abnormal tumor marker levels. A high level of the tumor marker CA-125, for instance, suggests, but doesn't confirm, the presence of ovarian cancer.

Tumor markers can be used to help diagnose cancer, predict response to therapy, check response to treatment, and determine if cancer has recurred. One tumor marker, prostate specific antigen (PSA) is commonly used to screen for prostate cancer in men who have no symptoms of the disease. (However, its presence can indicate conditions other than cancer, such as a urinary tract infection.) Markers have not yet been found for every form of cancer. Scientists continue to study tumor markers in order to develop more accurate and specific ways of detecting and diagnosing cancer.

Risks of Screening

Although screening would seem to be a sensible precaution against many forms of cancer, it too has risks:

• Overdiagnosis. Screening may detect cancers that would not actually harm people in their lifetimes, causing them to have unnecessary, and possibly harmful, surgery.
• False positives. Cancer screening tests can suggest cancer where there is none.
• False negatives. Screening tests can miss cancers, causing people to not get necessary treatment.

Doctors almost never refer to someone's cancer as being cured. Instead, they'll say it's in remission. Remission is defined as a decrease in or disappearance of the signs and symptoms of cancer. In partial remission, some of the signs and symptoms of cancer have disappeared, but not all. In complete remission, all signs and symptoms have disappeared. Complete remission does not necessarily mean that there is no cancer left in the body: there may be microscopic collections of cancer cells that can't be detected by current methods. But the longer the patient is in remission, the greater the chances that the cancer has been completed eradicated.

Cancer Survival Rates

Cancer survival rates show the percentage of people who survive a certain type of cancer for a specific amount of time. Doctors sometimes refer to a 5-year cure survival rate or a 10-year survival rate. For example, the 5-year survival rate for prostate cancer is 99%. That means that of all men diagnosed with prostate cancer, 99 of every 100 lived for 5 years after diagnosis. As cancer treatment advances, people with cancer are living for longer and longer periods of time. Survival rates are now quoted for 10, 15, or even 20 years.

Overall and relative survival rates don't tell you if the cancer survivors have achieved remission or are undergoing treatment. There are other survival rates that give more specific information:

• Disease-free survival rate is the number of people who have achieved remission.
• Progression-free survival rate is the number of people who still have cancer, but their disease isn't progressing.

Limitations of Survival Statistics

Survival rates are useful tools for understanding a prognosis and developing a treatment plan, but they have limitations. Survival rates are a generalization: they're based on studies of hundreds or thousands of people, all of whom are different in some way from the patient looking at the data. They may be younger or older, they may be in better or worse general health, and their cancer may have been diagnosed in its early or late stages. Moreover, survival rates are always outdated. The people included in the latest cancer statistics were diagnosed with cancer more than 5 years ago, and so didn't benefit from any recent advances in cancer treatment.

Using Statistical Information, or Not

Some patients might choose not to look at survival rates at all and decline to discuss them with their doctors, and this is a perfectly legitimate choice. Survival statistics can be confusing and frightening at a time when having a positive attitude is very important.

But if cancer patients do choose to look at statistical information in order to understand more about the prognosis for their type of cancer, it's important for them to be as knowledgeable as possible. The more people know about the type, grade, and stage of their cancer, the more closely they can predict their risk. Often physicians can help interpret the numbers and put the statistics in perspective.

Lifestyle and Cancer

Lifestyle has a profound effect upon whether someone gets cancer or not. This is demonstrated by the fact that several cancers that are extremely common in the US (colorectal, prostate, and breast cancer) are relatively rare in other parts of the world. Moreover, when people from other parts of the world move to the US, within a generation their cancer rates are close to those of families have lived in the US for generations.

Why is lifestyle, including diet, weight, and exercise, so important? The answer may lie in our genes. Environmental factors, like cigarette smoke, can cause damage to genes. But most cells injure their own DNA accidentally, by producing damaging free radicals as byproducts of normal metabolism. The damage that they cause, however, doesn't necessarily lead to cancer. What can cause tumorous growth are mutations to genes called proto-oncogenes and tumor-suppressor genes.

Oncogenes and Tumor-Suppressor Genes

Every cell contains genes called proto-oncogenes as well as tumor-suppressor genes. Proto-oncogenes are cell growth promoters, and they can be turned into oncogenes by mutations. Oncogenes turn normal cells into cancer cells by releasing an unending stream of growth-stimulating molecular signals, which stimulate cells to reproduce without stopping. Tumor-suppressor genes, on the other hand, stop cell growth. Mutations can cause their growth-stopping signals to be silenced, so that, again, the cell divides endlessly. There are other genes involved in the regulation of cell growth. Some cause cells that are damaged or abnormal to kill themselves. If these genes mutate, damaged cells will continue to reproduce.

The Western Lifestyle

Three factors in the Western lifestyle seem to increase a persons risk for cancer by encouraging mutations to proto-oncogenes and tumor-suppressor genes: diet, overweight, and inactivity. A Western diet is full of mutagens (chemicals that cause cells to mutate), for instance, in red meat cooked at high temperatures. Body fat secretes inflammatory chemicals into the bloodstream that can stimulate the growth of cancer cells. Being active actually lowers the levels of these growth-stimulating chemicals in the blood.

The Good News

There is a positive side to this information: lifestyle is something we can control. By making important changes in our lifestyle, we can hugely reduce our risk of cancer.

1. Don't Use Tobacco

Smoking is the single biggest cause of cancer in the world. All tobacco use causes cancer; it isn't safe to take tobacco as snuff or as chewing tobacco. Besides lung cancer, smoking also causes cancer of the mouth, throat, esophagus, larynx, cervix, bladder, pancreas, kidney, and stomach. It may also promote colon and breast cancer. About 3 million people die of smoking-related causes every year worldwide, and that number will rise to 10 million in the next century if the number of smokers continues to increase.

Even if you don't smoke, you can still be harmed by secondhand smoke, which kills thousands of people every year. Avoid people who smoke and smoke-filled areas.

Lung cancer is now the number-one cancer worldwide. If everyone quit smoking, the number of people who die from cancer would drop by at least one-third, and lung cancer would once again become the rare disease that it once was.

2. Eat a Healthy Diet

There's a great deal of evidence that the typical Western diet, high in red meat and animal fats, and low in fiber, fruits, and vegetables, is a major risk factor for cancer.

3. Maintain a Healthy Weight and Be Active

There's a clear link between obesity and cancer. In fact, one study by the American Cancer Society found that the heaviest people, compared with the leanest, had a significantly increased risk of death from 10 different kinds of cancer in men, and from 12 different kinds in women. Exactly how overweight causes cancer is still unclear. One reason might be that obesity leads to high levels of a growth factor called IGF-1, which is similar to insulin and inhibits cell suicide. IGF-1 might promote the growth of early cancers.

The answer may also lie in the body's inflammatory response. Fat cells release inflammatory chemicals called cytokines into the bloodstream that can stimulate the growth of cancer cells. The more overweight someone is, the greater the level of cytokines, and the greater the chance that precancerous cells will become cancerous.

Exercise has a proven protective effect against cancer. Regular physical activity lowers the levels of both IGF-1 and cytokines in the bloodstream, and it does this even if the person who exercises remains overweight. The lower levels of these cancer promoters are one possible explanation for the protective effect of regular exercise. In addition, estrogen levels in the blood are lowered by regular exercise in women, and this may be why exercise helps protect against getting breast cancer. People should try to be physically active for 30 minutes or more on most days of the week.

4. Protect from the Sun

Skin cancer, or melanoma, is both very common and very preventable. Sun exposure is the most frequent cause, so it pays to protect against the sun:

• Avoid peak radiation hours (10 am-4 pm)
• Stay in the shade
• Cover exposed areas and wear a hat
• Use a broad-spectrum sunscreen with a sun protection factor (SPF) of at least 15 - Don't use indoor tanning beds or sunlamps. There's no such thing as a healthy tan.

5. Get Immunized

Certain viruses are associate with specific cancers. Fortunately, there are vaccines available to immunize against these viruses:

• Hepatitis B can increase the risk of developing liver cancer. All babies and some high-risk adults should be vaccinated.
• Human papillomavirus (HPV) is a sexually transmitted virus that can lead to cervical cancer. A protective vaccine is recommended for girls ages 11-12, and for girls and women ages 13-26 who haven't completed the full vaccine series.

6. Avoid High-Risk Behaviors

Viruses associate with certain types of cancer can be transmitted sexually or by sharing contaminated needles, so it's important to use condoms and not share needles.

• HPV is associated with cervical cancer and also cancers of the anus, penis, throat, vulva, and vagina. The more sexual partners a person has in his or her lifetime, the more likely that person is to have HPV.
• Human immunodeficiency virus (HIV), which can lead to AIDS, increases risk of anal cancer, cervical cancer, liver cancer, lymphoma, and Kaposi's sarcoma. People with many sexual partners and intravenous drug users who share needles have an increased risk of HIV.
• Hepatitis B and C increase the risk of liver cancer. Both hepatitis B and hepatitis C can be transmitted through sexual contact with an infected person or sharing needles with an infected drug user.

7. Have Regular Screenings

Regular screening and self-examination for certain types of cancer can increase the chances of discovering cancer early, when the chances of treating it successfully are greatest. Areas of the body that should be screened include the skin, mouth, colon, and rectum. Women should have regular cervix and breast screening. Men should have screening for the prostate and testes.

It's estimated that diet causes about one-third of all cancer cases, almost as many as tobacco. The importance of diet in preventing cancer was shown in a study that tracked patients with colorectal cancer. After their cancer had been surgically removed, these patients were followed for 5 years. Those who ate a traditional Western diet had a three times greater likelihood of having their cancer recur than those who ate a healthy diet, rich in fruits and vegetables and containing only small amounts of red meat. The Western diet stimulated the growth of the cancer cells that remained in their bodies.

Eating a healthy diet can't ensure that you don't get cancer, but it can greatly decrease the chances that you do:

• Eat an abundance of foods that come from plants: fruits, vegetables, nuts, whole grains, and beans. Study after study has shown that people who eat the most fruits and vegetables have the lowest rates of most cancers. Fruits and vegetables contain large amounts of antioxidants and fiber, which are important in preventing cancer. Many phytochemicals (plant chemicals) have been shown to fight cancer, and scientists are discovering new phytochemicals every day.
• Limit fat, especially animal fat. A diet high in animal fat, especially from red meat, is a risk factor for prostate and colon cancer. A high-fat diet may also be linked with breast cancer.
• Do use olive oil instead of butter and other fats. Olive oil is rich in oleic acid, which suppresses an oncogene that plays a key role in several human cancers.
• Drink alcohol in moderation, if at all. The risk of getting many different types of cancer increases with the amount of alcohol you consume. "Moderate" means two drinks a day for men, one drink a day for women.
• Don't cook meat at high temperatures, especially over an open flame. Doing so creates compounds known to promote certain cancers. An occasional barbeque probably won't hurt you, but don't do it too often.
• Avoid eating red meat and processed meat. Substitute poultry, fish, or vegetable sources of protein instead. The more red meat and processed meat that is consumed, the greater the risk of cancer.
• Eating oily fish, such as salmon, mackerel, sardines, and trout, has been linked to a lower incidence of breast and prostate cancer.

The Cancer Patient Diet

Maintaining weight while undergoing treatment for cancer can be difficult: patients may experience lack of appetite, nausea, vomiting, constipation, and diarrhea. But stabilizing body weight is very important, because doing so can help to support the immune system, lessen fatigue, and aid recovery. It helps to:

• Focus on quality, not quantity, of food.
• Drink nutritious beverages like milkshakes and liquid supplements.
• Eat a number of small meals a day, not three big ones.
• Keep high-calorie snack foods handy.
• Drink fluids between meals instead of with them.