Ploidy in invasive colorectal cancer. Implications for metastatic disease.

A retrospective study was performed to determine the ploidy of superficial (above muscularis propria) and deep (below muscularis propria) biopsy specimens from the primary colorectal cancer of 88 patients with Dukes Stage C2 and D colorectal tumors. The ploidy of lymph node and liver metastases was compared with that of the superficial and deep specimen from the corresponding primary tumor. Among the tumors studied, 78% exhibited nondiploid stemlines. In 19% of the tumors, the ploidy of the superficial biopsy differed from that of the deep biopsy. Among these discordant tumors, all of the deep biopsy specimens corresponded in ploidy to the liver metastases, whereas most of the superficial specimens were similar in ploidy to the lymph node metastases. Our observations suggest that measurement of a single site may not be sufficient to detect nondiploid stemlines within a tumor. They also suggest that measurement of deeper parts of invasive tumors may be more reflective of the phenotype of distant metastases than measurement of superficial specimens.