Perianal metastasis from a sigmoid carcinoma--objective evidence of a clonal origin. Report of a case.

A case is described in which flow cytometric DNA analysis of a sigmoid cancer and a subsequently diagnosed anal malignancy demonstrated the same DNA aneuploid pattern in both tumors. The ability to show, by this technique of DNA analysis, that an anal malignancy has seeded from a colon cancer could be important for future therapy. This is because the positive identification of such a deposit as a "dropped" metastasis would prevent inappropriately radical surgery.