Digestive system melanoma refers to a melanoma starting in the stomach, intestines, salivary glands, mouth, esophagus, liver, pancreas, gallbladder, or rectum. Melanoma is a disease in which malignant (cancer) cells form in the melanocytes. Melanocytes are commonly found in the skin and are the cells that give the skin color. While it is not uncommon for melanomas to start in the skin and later spread to other parts of the body (metastasize), melanomas originating in the gastrointestinal tract are rare. The most frequently reported site is in the esophagus and anorectum.

Symptoms of a digestive system melanoma may be nonspecific, including blood in the stool, stomach pain, vomiting, diarrhea, weight loss and anemia (low red blood cell count). The cause of digestive system melanoma is not well understood. Some researchers theorize that it may have originated from an undetected primary tumor.

Treatment may include surgical excision of the gastrointestinal tract involved, chemotherapy, and immunotherapy.

• The cancer originated from a undetectable primary tumor that spontaneously (naturally) regressed on its own
• The cancer originated from a primary tumor that is so small it can not be detected using standard clinical and laboratory investigations
• Early melanocyte cells (not usually found in the digestive system) lost their way during the development of the baby in the womb, and that these misplaced cells later became cancerous

A variety of imaging tests may be involved in the initial detection of the tumor, including: video capsule endoscopy, ultrasound, PET scan, and CT scan. The tumor is confirmed by surgical resection. Careful study of tissue samples from the tumor under a microscope will show the same immunohistochemical characteristics of skin melanomas. Once this has been established, the following are proposed diagnostic criteria for primary melanoma of the small intestine:

1. The identification of a single solitary melanoma in the mucosa of the digestive system
2. The presence of other melanoma in the surrounding areas of the digestive system
3. The absence of cutaneous melanoma or other atypical skin tumors in the melanocytes