A better prognosis for Merkel cell carcinoma of unknown primary origin

Background There is limited evidence that Merkel cell carcinoma (MCC) arising from a nodal basin without evidence of a primary cutaneous (PC) site has better prognosis. We present our experience at 2 tertiary care referral centers with stage III MCC with and without a PC site. Methods Fifty stage III MCC patients were identified between 1996 and 2011. Clinical data were analyzed, with primary endpoints being disease-free survival and overall survival. Results Of stage III patients, 34 patients presented with a PC site and 16 patients with an unknown primary (UP) site. Treatment strategies varied; of patients with UP vs PC sites, 25% vs 44% underwent combined regional lymphadenectomy and radiation, with an additional 25% vs 15% receiving chemotherapy. The median disease-free survival for a UP site was not reached vs 15 months for a PC site (hazards ratio =.48, P =.18). The median overall survival for a UP site was not reached vs 21 months for a PC site (hazards ratio =.34, P =.03). Multivariate analysis showed that UP status was a significant factor in overall survival (P =.002). Conclusions Stage III MCC with a UP site portends a better prognosis than MCC with a PC site.