Bowel cancer types

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The three main areas of large bowel cancers are the:-

• Colon
• Rectum
• Anal canal and anal margin

For colon and rectum 95% are adenocarcinomas (cancer started in the glandular tissue in the lining of the bowel). For anal margin most are squamous cell carcinoma (originating in skin tissues). Any of these sites can also have other rare types of tumours. This section does not address the very rare small bowel cancer.

Adenocarcinomas: As mentioned above adenocarcinomas account for 95% of colorectal cancers. In the case of adenocarcinomas the malignancy started in glandular tissue of the bowel. There are two particular types of adenocarcinoma of the colon and rectum:

• mucinous carcinoma - a type of cancer that begins in the glandular tissue of internal organs and produces mucin (the main component of mucus)
• signet-ring carcinoma- the term describes how the cells of this particular tumour type appear under the microscope (the cells form in the shape of a signet ring); signet ring carcinomas are considered more aggressive than regular adenocarcinomas; they are quite an uncommon type

Squamous cell cancers: Squamous cells are the skin-like cells that make up the bowel lining. These cells are mainly found around the anal canal and anal margin and are treated very differently to rectal and colon cancers. 

Carcinoid tumours: Carcinoid is a tumour of the endocrine system ( network of glands containing neuroendocrine cells that produce hormones). This is a rare type of cancer which is most commonly found  in the digestive system, particularly in the appendix or the small bowel (intestine). Very rarely they are found in other parts of the body. This type of cancer develops very slowly and it may take several years before the carcinoid is diagnosed.

Sarcomas: Sarcomas are cancers of the connective or supportive tissue of the body (bone, muscle, fat, cartilage etc.). With colorectal cancer typical subtype is leiomyosarcomas which is a type of malignancy that started in the muscle of the bowel.

Lymphomas: Lymphoma is a cancer that starts in the lymphatic system. Lymphomas is considered to be a rare type of colorectal cancer (only about 1 in 100 cases of colorectal cancers are lymphomas)