An isolated Merkel cell carcinoma metastasis at a distant cutaneous site presenting as a second 'primary' tumor.

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma of the skin. Disease progression usually occurs via lymphatic spread to regional lymphatic draining basins, followed by distant metastasis. We report the clinical course, histopathology and genetic analysis of a 69-year-old woman with likely hematogenous spread of cutaneous neuroendocrine carcinoma manifesting as a single metastatic lesion to a distant cutaneous site. Although the possibility of two cutaneous primary MCCs was considered, array comparative genomic hybridization (aCGH) identified identical distal amplification of a region of chromosome 12p, and synchronous loss of chromosomes 8p and 17p, effectively ruling out the possibility of independent primaries. We propose that this represents a primary cheek MCC with rapid, isolated cutaneous metastasis to the contralateral ankle via hematogenous spread. The distinction between a second primary MCC and a distant cutaneous metastasis clearly has important implications with regard to staging, treatment and prognosis. To our knowledge, this represents the first report of the use of aCGH to clarify the relationship of multiple synchronous cutaneous MCCs and the first report of a single distant cutaneous focus of hematogenous spread. Our data calls into question prior reports alleging multiple cutaneous primaries of this very rare tumor.