Merkel Cell Carcinoma Metastases to Caruncle With Orbital Extension: Report and Literature Review

Merkel cell carcinoma (MCC) is an uncommon and aggressive skin cancer of neuroendocrine origin. The tumor usually presents with a locoregional spread and most frequently metastasizes to the skin, liver, bone, lung, and brain. Despite the orbit being a relatively common site of metastases, it has rarely been reported in patients with MCC. The authors present a case of biopsy-proven orbital metastatic MCC in an 86-year-old male who presented with a rapidly enlarging right caruncle/subconjunctival mass with orbital extension and a history of forearm MCC excision 3 years prior. There are only 3 reported cases of distant metastatic MCC to the orbit, all presenting as a mass originating from extraocular muscles; and no cases of caruncle involvement. Merkel cell carcinoma orbital metastases have been infrequently described in the literature. The authors present a case of an anterior orbital mass 3 years after total excision and radiotherapy to a forearm lesion. Clinicians should be mindful about this possibility and keep metastatic Merkel cell carcinoma within differential of a metastatic orbital lesion.