Abstract

Cutaneous carcinosarcoma, known for its biphasic composition of intimately admixed malignant epithelial and mesenchymal cell populations, is a rare cutaneous tumor. In contrast to systemic carcinosarcoma occurring in other organs of the body, cutaneous carcinosarcoma is associated with a more favorable prognosis and overall low metastatic rate. While various etiologies have been proposed, including monoclonal, polyclonal, and collision tumor origins, the most accepted hypothesis currently is the ‘divergence’ or ‘monoclonal theory’ which postulates that the malignant epithelial component undergoes a genetic alteration leading to sarcomatous transformation. Herein, we present a compelling case of this rare entity in an 85-year-old male, who presented with a scalp mass. A wide-local excision was performed and revealed a biphasic tumor composed of irregularly-shaped nests and lobules of atypical squamous cells seamlessly associated with a high-grade spindled cell tumor component. Numerous mitoses, many atypical, were observed in each tumor cell component. Immunohistochemistry showed strong pan-keratin and cytokeratin-5/6 positivity in the epithelial/squamous cell component, including cells intimately surrounded by high-grade sarcoma. These keratin markers also highlighted scattered, dispersed spindled cells within the sarcomatous component. Of performed mesenchymal markers, SMA stained the sarcomatous component most convincingly. The overall findings were consistent with cutaneous carcinosarcoma/metaplastic carcinoma. If primary to skin it is important to note that – despite evidence of a high-grade malignancy – this tumor may in fact retain a fairly favorable prognosis.  However, integrated cooperation across many medical specialties is often required for proper diagnosis.