Factors influencing the development of sigmoid colon cancer. Bacteriologic and biochemical studies.

Background: Cancer of the sigmoid colon is especially sensitive to environmental factors such as food. The authors have conducted a series of studies with food as the external environmental factor and intestinal microflora as the internal environment factor in relation to sigmoid colon carcinogenesis.

Methods: Thirteen males who had previously undergone surgery for sigmoid colon cancer, and who later developed new epithelial neoplasia of the colon, were chosen as the high risk (HR) group. Fourteen males of similar age, whose large bowel was entirely normal by total colonoscopy, were chosen as the control (CONT) group. Food constituents were analyzed by a dietician. Fecal bile acids, cholesterol metabolites, degradation products of amino acids, pH, water content, and bacterial flora were quantitatively analyzed.

Results: Although the HR group consumed slightly more carbon hydrate, fiber, and calcium, as a whole, there was no significant difference in food constituents, especially animal fat, between the two groups. Concentrations of bile acids and cholesterol metabolites were not different between the groups, with the exception of a higher level of cholestanol in the HR group. Succinic, lactic, propionic, and isovaleric acids were abundant in the HR group. Fecal pH and amounts of hydrogen sulfide and cresol also were higher in the HR group. The total amount of bacteria, lecithinase-negative Clostridia, and Lactobacillus, were also more abundant in the HR group.

Conclusions: The feces of the HR group was abundant in such substances as sigmoid colon cancer promoters, and appeared unrelated to food constituents. Resident flora of the HR group were abundant in enzymatically active anaerobes. Because agents carcinogenic to the colon and rectum exist ubiquitously, microflora play a key role in sigmoid colon carcinogens by producing promoters.