Adenocarcinomas are tumors that start in the lining of internal organs. "Adeno" means gland. These tumors start in cells with glandular properties, or cells that secrete. They can form in many different organs, such as the lung or the breast. In colorectal cancer, early tumors start as small adenomatous polyps that continue to grow and can then turn into malignant tumors. The vast majority of colorectal cancers are adenocarcinomas.

These are tumors that start in the muscle tissue of the digestive tract, although they rarely appear in the colon. They can be benign (noncancerous) at first, but many do turn into cancer. When this happens, they are called sarcomas. Surgery is the usual treatment if the tumor has not spread.

Learn more about GIST.

A lymphoma is a cancer that typically starts in a lymph node, which is part of the immune system. However, it can also start in the colon or rectum.

Learn more about Hodgkins lymphoma, Non-Hodgkins lymphoma, and cutaneous lymphoma.

Carcinoids are tumors that start in special hormone-producing cells in the intestine. Often they cause no symptoms. Surgery is the usual treatment.

Turcot syndrome is a rare disorder that includes colorectal polyposis, colon cancer, and brain tumors. Mutations in different genes have been found in individuals with this syndrome, including mutations in the APC, MLH1, and MSH2 genes. For this reason, Turcot syndrome is said to be genetically heterogeneous.

Peutz-Jeghers syndrome is an autosomal dominant disorder that is associated with the following characteristics:

• Melanocytic macules (dark blue or brown moles)
  These moles can be located around and/or in the mouth including the lips, and around the eyes, nostrils, and anus. Dark moles may also appear on the fingers. The lesions may fade by adulthood.
• Multiple polyps in the gastrointestinal tract
• Increased risk of benign (noncancerous) tumors of the ovaries and testes
• Increased risk of cancers of the stomach, esophagus, breast, colon, and pancreas
• Peutz-Jeghers syndrome is caused by mutations in a gene on chromosome 19 known as STK11, which functions as a tumor suppressor gene.

Learn more about Peutz-Jeghers syndrome.

Up to 15% of colorectal cancer patients have family members with colorectal cancer, but do not have a known colorectal cancer syndrome such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colon cancer (HNPCC). Colon cancer in these families may appear to follow an autosomal dominant pattern of inheritance. As genetic research continues, genes may be identified to explain these family histories.

This rare, childhood-onset disease is an autosomal dominant disorder that results from mutations in various cancer susceptibility genes, including the SMAD4/DPC4 and BMPR1A genes. The condition is associated with the development of hamartomatous polyps (few to numerous) that can be present throughout the gastrointestinal tract.

Symptoms can include:

• Diarrhea
• Hemorrhage
• Protein-losing enteropathy

Juvenile polyposis is associated with an increased chance for gastrointestinal and pancreatic cancers. Most patients appear to be sporadic cases (happening for the first time in a family). However, this may actually be the result of decreased penetrance (i.e., the causative gene mutation is present in one of the parents but the symptoms did not develop).