Biopsy-Proven Metastatic Merkel Cell Carcinoma to the Orbit: Case Report and Review of Literature.

Merkel cell carcinoma is a rare neuroendocrine tumor of subspecialized dermal mechanoreceptors, associated with immunosuppression. The usual ophthalmic presentation is an eyelid lesion. The authors present a case of biopsy-proven orbital metastatic Merkel cell carcinoma in the absence of any eyelid lesion, in an immunosuppressed patient with a history of multiple cancers. There are to the authors' knowledge only 2 other case reports of presumed metastatic Merkel cell carcinoma to the orbit, though neither were biopsied. Despite its rarity, metastatic Merkel cell carcinoma should be included in the differential of a metastatic orbital lesion, in the patient with a known or suspected cutaneous primary. The patient has had an excellent response to combined radiotherapy and programmed death-1 inhibitor pembrolizumab, and this case highlights the potential benefit of an exciting new biologic therapy.