Diploid predominance in hereditary nonpolyposis colorectal carcinoma evaluated by flow cytometry.

Fifty-nine colorectal carcinomas of patients with verified cancer family syndrome (CFS) were analyzed for DNA ploidy using flow cytometry. Sixty-eight percent of the tumors were diploid, and 32% were aneuploid. The aneuploid tumors had a median DNA index of 1.24 (range, 1.12-1.97). In 90% of all tumors the DNA index was less than 1.27. This predominance of diploid/near-diploid tumors was seen both in primary and in metachronous carcinomas. In 21 cases a cell cycle analysis was possible. Tumors with the S-phase fraction (SPF) greater than or equal to 9.8% had a worse prognosis than tumors with the SPF of less than 9.8%. These findings suggest that the predominance of diploid/near diploid DNA values is one of the characteristics of colorectal carcinomas in CFS. This might signify the existence of two or more pathogenetically different subgroups of colorectal carcinoma and explain the proposed better prognosis of colorectal carcinoma in CFS compared with other colorectal carcinomas.