Merkel cell carcinoma of unknown primary site; case presentation and review of the literature

•Unknown Primary Merkel cell carcinoma is a rare NET, which usually presents with extensive lymph node involvement.•This tumor follows a more indolent natural course than a Merkel cell carcinoma of known primary and of similar staging.•Surgical excision with R0 resection remains a common practice in the management of unknown primary Merkel cell carcinoma.•Adjuvant chemotherapy after R0 resection is the usual practice, despite the lack of good quality literature evidence.

Merkel cell carcinoma (MCC) is a rare skin malignancy associated with sun exposure and considered as a Neuroendocrine Tumor due to its characteristic histologic features. However there is increasing number of reports of Unknown Primary MCC's (UPMCC). Although initially UPMCC was considered a variant of known primary MCC, there is growing evidence that it could represent a different clinical entity.We present the case of a 60 year-old male patient who was referred to our department for surgical management of lymph node disease for UPMCC. The patient had undergone excisional biopsy of an inguinal lump, which was found to be an infiltrated lymph node by MCC. The patient underwent full imaging staging including a PET/CT, which failed to identify a primary site, and revealed only intra-abdominal lymph node disease. The patient underwent extended retroperitoneal and inguinal lymph node dissection and remains free of recurrence 16 months postoperatively.