HPV-associated carcinosarcoma of the anal canal: A rare case provides insight into the pathogenesis of these biphasic neoplasms.

Carcinosarcomas are biphasic malignant neoplasms and are rare outside the corpus uteri. Here we report a carcinosarcoma arising in the anal canal in a 60 year-old female. This is only the fourth reported case of a carcinosarcoma arising at this site, the second reported case with molecular evidence of high risk HPV association, and the first case with reported cytogenetics analysis. The finding of high risk HPV in both the epithelial and mesenchymal components of the tumor provides important insight into the pathogenesis of the tumor, and strongly suggests that both components of this carcinosarcoma are derived from a common immature epithelial progenitor cell during tumorigenesis.