Merkel cell carcinoma with divergent differentiation: two case reports.

Merkel cell carcinoma (MCC) is a rare primary neuroendocrine carcinoma of the skin, usually occurring at sun-exposed sites in the elderly. Divergent differentiation in MCC, though rare, has been reported in previous case series. We describe two new cases of MCC with divergent differentiation. Case 1 was a 96 year-old male with a scalp lesion; on biopsy, the morphology and immunoprofile suggested MCC with divergent squamous differentiation. Case 2 was an 87 year-old female, with a lesion on the leg, originally reported as squamous cell carcinoma, later showing extensive local recurrence. On review, primary histology showed a Merkel cell carcinoma with divergent differentiation, most likely trichilemmal carcinoma; the recurrence showed only MCC. These cases illustrate that Merkel cell carcinoma is capable of divergent differentiation, including squamous and adnexal morphologies. Correct diagnosis is essential for appropriate prognosis and management, as later recurrence or metastases may only show the Merkel-cell component.