The risk of a second primary cancer occurring in five-year survivors of an initial cancer.

Patients with a greater than five-year survival diagnosed with cancer of the stomach, colon, breast and uterus (included in situ) at the Kanagawa Cancer Center from 1963 to 1980 were studied for multiple primary cancers. They were followed up to December 31, 1985, for the occurrence of second primary cancers by means of a record linkage to the population-based cancer registry in Kanagawa Prefecture. The occurrence rate of total second primary cancers was 2.6% (76/2,977). Among the first primary cancer sites, the rate for cancer of the colon was highest: 5.3% (5/94), and the rate for women with cancer of the uterus lowest: 1.4% (16/1,146). The number of observed second primary cancers was compared with the expected number, which was calculated by the person-years method, to obtain an estimate of the risk. The relative risks (RR: observed: expected value) of women with cancer of the breast were significantly high for developing cancer of the colon (RR, 3.7), cancer of the opposite breast (RR, 3.9) and cancer of the ovary (RR, 5.8). Men with cancer of the stomach had a significant risk of developing cancer of the colon (RR, 3.3). It may be considered, at least in part, that some cancer patients, especially those with cancer of the breast, have a high risk of a second primary cancer occurring. These results may provide clues and information to the etiology of predisposition to and prevention of cancer.