Metastatic Basal Cell Carcinoma Arising From a Primary Cutaneous Carcinosarcoma

Primary cutaneous carcinosarcoma is a rare malignant tumor composed of both an epithelial and mesenchymal cell population. We present a case of a man, aged 56 years, found to have a 26-mm exophytic lesion on the vertex scalp identified to contain a distinct population of basal cell carcinoma (BCC) as well as another population of spindled cells representing a poorly differentiated sarcomatous component. Five years after the removal of the primary lesion, the patient presented with metastatic BCC to the right scalp, right cervical nodes, lung, and rib. Next-generation sequencing of the lung metastasis was performed, revealing mutation of the patched gene (PTCH1) and prompting treatment with vismodegib (Erivedge). Cases of primary cutaneous carcinosarcoma with a basal cell epithelial component are rare and not much is known about their pathogenesis or clinical course. This case is unique in that metastatic BCC arose from a primary carcinosarcoma in which the carcinomatous component was basal cell. Furthermore, it has clinical significance in the successful use of a selective hedgehog pathway inhibitor.