Cancer of the large intestine is far more common than cancer of the small intestine, because transit time is progressively slowed by fluid re absorption to form a semi solid stool, thus increasing contact exposure to fecal carcinogens.
Cancer of the large intestine is also much more common in the Western world than in less sophisticated communities. There is circumstantial evidence that the lack of fiber roughage is sophisticated diets id responsible for this difference.
A high proportion of indigestible cellulose fiber is through to lead to healthy bowel evacuation, removal of this roughage by moder food processing technology result in small stools, chronic constipation, and prolonged exposure of the colorectal mucosa to fecal carcinogens.
These have been identified in part as nitrosamines, produced from ingested nitrate and bacterial action in a constipated large bowel, and it has been established that their formation can be blocked by an adequate intake of vitamin C acts as a laxative, and thus decreases the time of exposure of the colon and rectum to the action of the fecal carcinogens.
There are some other predisposing factors in colorectal cancer. Patients with familiar colonic polyposis almost invariably develop colonic cancer at some time in their adult life. Patients with uncontrolled ulcerative colitis for 10 or more years very frequently succumb to colonic cancer, and because of the very long duration of bowel symptoms the transition to malignancy is usually almost impossible to perceive.
Vitamin C ingestion has been shown to induce regression in colonic polyposis, and it is reasonable to assume that it would also afford some protection in ulcerative colitis, although we are not aware of any specific studies in the atter area. The symptoms of large bowel cancer depend upon whether the tumor is in the right colon, the left colon, or rectum.
In the right colon the bowel caliber is relatively large and the bowel contents are fairly fluid, and therefore obstructive symptoms rarely occur. The usual symptoms of a cancer of the right colon are rather vague blend of anemia from blood loss from the tumor, weight loss from the systemic toxemia of an ulcerated tumor constantly bathed in liquid feces, and often very little else.
The treatment is by wedge resection, the extend of the resection being governed by the blood supply and associated lymph node drainage at different sites.
Because tumors of the right colon tend to present themselves insidiously and tumors of the left colon more dramatically, by the time the diagnosis is reached liver metastases tend to be more common in the former group, with a correspondingly poorer overall prognosis.
Radiotherapy is quite useless in colonic cancer, because to irradiate such an intro abdominal target would result in unacceptable damage to the normal tissues. At the present time chemotherapy is widely used in inoperable situations, and although some useful retardation of tumor growth may sometimes be achieved the response is highly unpredictable and the side effects are so disagreeable as to make the value of the treatment doubtful.