Procollagen 1 expression in atypical fibroxanthoma and other tumors

Procollagen (PC) is secreted by fibroblasts into the extracellular matrix, where it is cleaved to form collagen. The rat anti-human PC-1 monoclonal antibody has been reported to react with atypical fibroxanthoma (AFX), a poorly differentiated but usually benign skin lesion common in elderly patients. We have studied PC-1 staining in 50 tumors with AFX histological features (four of which were subsequently reclassified as non-AFX tumors) to confirm this prior observation. In addition, we have investigated PC-1 in other skin tumors, particularly those with spindled cell or sclerosing/desmoplastic morphologies.

Archival material was retrieved and sections were prepared and immunostained with PC-1 as well as a panel of antibodies, including S-100 and MNF-116 (cytokeratins 5, 6, 7, 8, 17, and 19).

PC-1 staining was strongly positive in 40 of 46 (87%) AFXs. Three AFXs displayed weak staining with PC-1 even after repeat staining of 10 tumors that were initially weak. Three additional tumors stained with both PC-1 and MNF-116 and were classified as AFX-like squamous cell carcinoma (SCC). One tumor with AFX-like histology was PC-1 negative and S-100 positive and was classified as an AFX-like melanoma. Positive staining in tumor cells was observed in three of nine (33%) desmoplastic malignant melanomas, three of eight (38%) desmoplastic SCCs, zero of 10 (0%) desmoplastic trichoepitheliomas, zero of 10 (0%) morpheic basal cell carcinomas, and zero of 10 (0%) sclerosing sweat duct carcinomas.

PC-1 is a useful antibody in a diagnostic immunohistochemical panel when investigating AFX and AFX-like tumors; however, good technical quality and careful interpretation are necessary when using a panel of antibodies, particularly to keratin and S-100 protein, for optimal accuracy.