Merkel Cell Carcinosarcoma With a Bland Sarcomatous Component

Merkel cell carcinoma with a sarcomatous component is very rare, with only 12 cases reported in the literature, often with overtly malignant myoid differentiation. We report a case of metastatic Merkel cell carcinosarcoma presenting in a lymph node 6 months after a diagnosis of cutaneous Merkel cell carcinoma with conventional histologic features. The metastatic lesion showed a unique biphasic appearance with admixed populations of neuroendocrine epithelial cells and fascicles of mitotically active spindle cells with mild cytological atypia. In addition to the immunomorphological features, a common molecular profile between the epithelial and mesenchymal components further supported the notion of carcinosarcoma in this case. To the best of our knowledge, a bland sarcomatous component has not been previously described in Merkel cell carcinosarcoma, which can be easily overlooked as a reactive stromal reaction microscopically.