Less common tumours of the colon and rectum

Abstract

Although adenoma and adenocarcinoma constitute the most commonly seen neoplasms of the colon and rectum, other tumour and tumourlike conditions have been described. Some of these lesions are extraordinarily rare, and the therapeutic approach may therefore not be entirely clear. Others, while benign, may mimic malignant processes. Understanding the pathology and biology of each of these tumours is vital to implementing therapeutic interventions. Neuroendocrine carcinoma develops from endocrine cells distributed throughout the intestinal tract. In general, these tumours are extremely aggressive and are associated with a high rate of metastasis and a poor prognosis. Carcinoid tumours originate from enterochromaffin cells (part of the APUD system) and are the most common neuroendocrine neoplasms of the gastrointestinal tract (GI) tract. The behaviour and prognosis are highly variable and are affected by multiple factors including tumour size, depth, presence and location of metastases, and primary tumour location. The extent of surgical resection is based on the likelihood of residual primary disease, metastases in the lymph nodes, and whether tumour debulking may help to reduce the symptoms of the carcinoid syndrome. GI stroma tumours (GISTs) occur throughout the colon, but are most often located in the rectum. The use of imatinib mesylate (Glivec) in combination with surgical resection may help to reduce recurrence. A large variety of uncommon neoplasms arise from colonic mesenchymal tissues, including leiomyosarcomas and liposarcomas. The cell of origin of adenosquamous carcinomas is unknown, but histologically these tumours demonstrate a mixture of both glandular and squamous features. These are often aggressive tumours and have a poorer prognosis than adenocarcinomas. Primary melanoma of GI tract is very rare and occurs only in the anorectal area. Colonic melanoma is invariably presenting only as a site of metastatic disease. As long-term prognosis is extremely poor, radical surgery may not be warranted.