Carcinoma of Colon

Growth is a complex process, it involves mechanisms for starting and limiting cell-division. When the particular tissue reaches a size, appropriate to its function a number of processes may limit further growth, including; supply of material, production of material, oxygen supply and edge detection for neighbouring tissue. Theories of Cancer involve the possibilities of adversely affecting the processes of growth limitation. The achievement of autonomy in the growth process usually involves some damage to the genetic material in the cell, thought to be deletion of a gene switch for cell suicide in potentially dangerous DNA damage. The time scale for processes to become cancerous is about 20 years. Certain chemicals may affect either the rate of cell-division or the DNA damage or both. As those patients with liver failure demonstrate, the bowel contains some fairly toxic material and colon cancer is one of the commoner tumours.

The normal rate of cell-division in the bowel is very high and with replacement every 22 days is higher than a lot of cancers. There is a limit to this reasoning. Some of my teachers over the years have commented on the high cell turnover in the skin with psoriasis. When you consider the use of filtered ultraviolet and coal tar in the condition, it is amazing that the rate of skin malignancies in psoriasis is not higher.

Carcinoma of the colon has a greater incidence in the elderly and involves the distal colon or rectum more frequently than elsewhere (60%-70%). Colonic carcinomata have been found in patients in their third decade, so the diagnosis is part of the differential at any age. 20% of tumours occur below the age of 50 years. There is some predisposing factor; an inherited tendency or familial polyposis, such as Gardiners Syndrome. Where inherited factors are involved, the incidence of right sided tumours is a little higher. 2-5% of tumours are multiple, but this incidence of multiple tumours also rises to as high as 40% of cases in familial polyposes. The tumours are usually adenocarcinomas. Aetiological factors that have been discussed include constipation and high fat in the diet or obesity. The basic mechanism involves the greater risk of more prolonged contact of a higher concentration of harmful metabolites in the colon with cells that may have divided more frequently then the average.

Staging, Dukes classification:

• a, Bowel wall involved, but no extension beyond propria.
• b, Tumour extends beyond muscularis propria.
• c, Lymph node metastases are present.
• d, Distant metastases.

With nowhere else to put it, I have included one case of ileal carcinoma. There is no example of Carcinoid Tumour which would be a possibility in the ileo-caecal region.