A rare case of anal tumor: Anal carcinosarcoma

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.

A rare case of anal carcinosarcoma with human papilloma virus infection in both biphasic tumor elements: An immunohistochemical, molecular and ultrastructural study

Carcinosarcoma of the anus is rare and has yet to be reportedly associated with the keratinocyte-specific Human Papilloma Virus (HPV). We describe a case of anal carcinosarcoma with HPV infection in both the epithelial and mesenchymal components of the tumor by immunohistochemistry, chromogenic in-situ hybridization (CISH) and further supported by electron microscopy (EM). Microscopic examination of the tumor showed nests of poorly-differentiated invasive squamous cell carcinoma with basaloid features intermixed with a hypercellular, atypical spindle cell proliferation. Immunohistochemistry demonstrated that the epithelial component was positive for AE1/AE3, p63, CK5/6 and p16, whilst the mesenchymal component was positive for smooth muscle actin, vimentin, and focally positive for desmin and p16, consistent with carcinosarcoma. The tumor was negative for GATA-3, CK7 and CK20. CISH demonstrated that the tumor was positive for high risk HPV (subtype 16/18) in both tumor components. EM further supported the presence of intracellular virus particles (~50 nm) that is compatible with HPV infection. Infection of both epithelial and mesenchymal tumor components by HPV has not been previously observed in the gastrointestinal tract. This finding may represent initial epithelial HPV infection with subsequent divergent tumoral differentiation and suggests the presence of viral replication in both biphasic tumor components.