We have performed mass surveys for colorectal cancer by using an immunological fecal occult blood test (OC Hemodia) since April, 1987. In this report, we evaluated the mass survey protocol, and investigated the upcoming problems and measures.
The total number of examinees for six years until March, 1993 was 172, 474. The persons needed detailed examination amounted to 6, 952 (4.0%) and the persons received the detailed examination, 4, 706 (67.7%). A total of 144 colorectal cancer cases (detection rate: 0.08%, 153 lesions) were discovered, 93 cases (64.6%) were in their early stage. 101 cases (66.0%) of 153 lesions were early cancer, and 71 cases (70.3%) were cured by endoscopic polypectomy.
The detection rate of colorectal cancer was higher in males than females. In particular, the finding rate for males 50 years old and above was extremely high. We strongly recommend that the elderly people should receive a mass survey. Moreover, it is important to offer the opportunity for detailed examination to the persons who don't receive them. That might raise the detection rate.
It was found that detailed examination has left much room for improvement in terms of methodology. Some medical institutions performed only fecal occult blood testing. They are require d to raise the understanding of mass surveys for colorectal cancer. Collaboration with the medical institutions that are capable of detailed examination and care is indispensable to raise the accuracy of examination.
On the basis of the results in 1992, we calculated the diagnostic accuracy of immunological fecal occult blood test. The sensitivity of the one-day-method was 70.8%, the specificity, 97.0%, and the positive predictive value 2.1. The sensitivity of the two-days-method was 86.7%, the specificity, 95. 3%, and the positive predictive value, 2.7, and was better than the one-day-method.
These findings suggest that the carcinomas, negative to the occult blood test, still exist in a high frequency rate. Therefore, we should perform mass surveys by the two-days-method every year, in order to improve the evaluation of the mass survey method for colorectal cancer.