Multiple primary colorectal and gastric carcinoma in Japan.

We investigated the occurrence of multiple primary colorectal and gastric cancer (MPCGC) in 1277 colorectal cancer patients between 1972 and 1996. MPCGC was found in 65 (5.1%). In the 28 synchronous cases, gastric or colorectal cancer was accidentally detected by pre-, intra-, or postoperative examinations. In 23 of the 37 metachronous cases, colorectal cancer developed on average 83 months after the operation for gastric cancer. In the other 14 cases, gastric cancer developed on average 70 months after the operation for colorectal cancer. Therefore, careful pre-, intra-, or postoperative examinations are strongly called for in order to not overlook the presence of colorectal or gastric lesions in MPCGC cases.