PURPOSE: With advances in diagnostic techniques and treatment modalities, the number of patients identified with colorectal carcinoma who develop multiple primary malignancy during long-term follow-up has been increasing. We investigated multiple primary malignancies occurring in a large number of colorectal carcinoma patients who had undergone surgery in the 1980s at our institution. METHODS: A total of 1,304 Japanese patients with colorectal carcinoma treated between January 1980 and December 1989 were prospectively followed to investigate the situations in which multiple primary malignancies occurred. To determine whether the incidence of multiple primary malignancies in this series was higher than expected, we calculated the expected numbers of carcinoma occurrences and evaluated these findings by exact binomial test. RESULTS: The median follow-up period was 95 months. The incidence of multiple primary malignancy was 18.7 percent (143/765) among males and 14.7 percent (79/539) among females. The most common site of multiple primary malignancy among males was the stomach, followed by the lung, prostate, larynx, liver, esophagus, and urinary bladder. The most common site among females was the uterus, followed by the stomach, breast, and liver. The sites that showed a higher incidence of multiple primary malignancy than the expected value were: the prostate, larynx, urinary bladder, oral cavity/pharynx and thyroid among males, and the uterus and oral cavity/pharynx among females. CONCLUSIONS: Fifteen to 20 percent of Japanese colorectal carcinoma patients experienced multiple primary malignancies. Postoperative long-term screening methods should be established considering the actual occurrence numbers and risk rate of multiple primary malignancies in addition to metachronous colorectal carcinoma.
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