Abstract

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor that can metastasize to locoregional sites, lymph nodes, and distant organs. MCC metastasis to the site of an unrelated cutaneous malignancy has been only reported twice to our knowledge in a case of squamous cell carcinoma (SCC) and a case of dermatofibrosarcoma. A 77-year-old man with history of autoimmune disease and melanoma presented with MCC on the right eyebrow. This was managed by excision with negative margins and adjuvant local radiotherapy. Sentinel lymph node biopsy was negative. He subsequently developed in-transit disease. On follow-up, the patient presented with 3 additional papules suspicious for metastatic disease. Shave biopsy revealed concurrent unrelated cutaneous lesions overlying metastatic MCC in 2 of 3 biopsies, specifically seborrheic keratosis (SK) and basal cell carcinoma (BCC). Although the MCC closely approximated the unrelated cutaneous lesion, true intermingling of neoplastic populations (tumor-in-tumor phenomenon) was not observed. In both samples, the MCC was limited to the deeper aspect of the biopsy, raising the possibility that a more superficial sampling might have resulted in misdiagnosis with only the unrelated SK or BCC present for evaluation. The patient developed nodal disease and died of unknown causes approximately 15 months after his initial diagnosis. MCC has the potential to metastasize to sites of other skin tumors, which is distinct from “mixed” primary MCC tumors with features of both SCC and MCC. Our report adds to the evidence suggesting MCC metastases can present either mingled with, or immediately deep to, the second tumor. Clinical sampling for metastatic MCC should account for the potential deeper location of these tumors, with consideration for punch biopsy. Furthermore, during pathologic evaluation of metastatic MCC, the potential for sampling error due to a concurrent unrelated tumor superficial to the MCC should be kept in mind.

Financial Disclosure:
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