[A case of anal fistula cancer probably developing from intraluminal dissemination of rectal cancer].

A 63-year-old man with a history of anal fistula was admitted to our hospital because the anal pain didn't disappear after the operation. On digital examination, a hard mass measuring 3.0 cm in diameter was found at the anal canal. Biopsy of the mass showed moderately differentiated adenocarcinoma. Colonoscopy revealed another rectal cancer at 15 cm from anal verge. Biopsy of the tumor also showed moderately differentiated adenocarcinoma, resembling the anal canal tumor. Because the histological findings of both tumors were nearly identical, we considered that cancer cells from the rectal cancer had been implanted and developed the metastatic tumor in the anal fistula. The patient underwent anterior resection for the rectal cancer, and a local resection for the anal canal cancer. Immunohistochemical staining for Ki-67, p53, Muc2, CD10, CK-7, and CK-20 revealed similar patterns in both tumors. Additionally, genetic analysis for p53, K-ras, and MSI revealed similar patterns in both tumors. We may suggest from these results that cancer cells from the rectal cancer had been implanted and developed the metastatic tumor in the anal canal.