Screening and prevention of colorectal cancer in Haining County.

From September 15, 1977, to April 15, 1978, 450, 477 persons over the age of 7 years were screened for schistosomiasis; a subgroup of 198,950 over 30 years were screened for colorectal cancer. Seventy-five malignant colorectal tumors were discovered in the latter group, a positive rate of 37.69 per 100,000 (seven were colonic cancers, 14 rectal cancers, 20 polyps with cancerous change, and 34 carcinoids). Of this group, 2701 had various types of polyps and 5242 had definitive diagnostic schistosomiasis. History, physical examination, and an occult blood test are simple, useful methods for detecting late colorectal cancer but are of no value in preventive screening of early cases. While digital rectal examination is an important, effective method of diagnosing rectal cancer, the positive rate is one tenth that of rectoscopy. It cannot be used for mass screening because the examining finger cannot tolerate such constant use and is too short to discover higher tumors. The sequence of colorectal cancerous change found in our center was from normal intestinal epithelium to tumorigenic polyps or colorectal ulcer, to polyps with anaplastic change, to polyps with local cancerous change, to adenocarcinoma. Cancer was seen more frequently in villous and adenomatous polyps; these are called precancerous stages of colorectal cancer. No relationship between schistosomiasis and colorectal cancer was found.