Abstract
This is a study on the rate of positive biopsy in cases of colorectal cancer and possible causes of false-negative results. In our Institute, 327 patients with advanced carcinoma of the large intestine were operated radically in the period between January 1970 and June 1978. A preoperative endo-scopywith biopsy was performed in 179 patients among them. The biopsy was positive in 162patients (90.50) and negative in 17 (9.5%). If seen from the viewpoint of forms of cancer, f alse-negative results were obtained in one out of 24 cases of polypoid form (4.2%) and 16(10.5%) out of 152 cases of ulcerated form, but none in three cases of scirrhous form.There was a tendency that false-negative biopsies were seen more in the ulcerated form thanin polypoid one. In order to see the mode of exposure of the cancer on the surface of the anal margin, these ulcerated carcinomas were classified into three groups:(A) carcinomatous tissue was completely covered with mucosa, (B) carcinomatous tissue was partially exposed, (C) carcinomatous tissue was completely exposed. Among 16 cases with false-negative biopsy, six were (A), four were (B) and five were (C). There was one case with remarkable necrosis which could not be classified in this way. Above results may indicate that the mode of exposure of the carcinomatous tissue at the anal margin does not necessarily affect the rate of false-negative biopsy. Number of biopsy specimen taken from a cancer may play a role in a false-negative result, for existence of carcinomatous tissue was in only 378 (66.2 %) of total 571 biopsy specimens which were taken with the intention from the suspected part of the cancer. Actu-ally only one perticle was taken in seven out of 17 false-negative cases. Thinking of the existence of false-negative cases even in group (C), it will be necessary to take at least more than one biopsy perticle from different parts on the top of the elevated margin of the carcinoma. Exf olliative cytology will, also, be useful.
