Merkel cell carcinoma: Clinical outcome and prognostic factors in 351 patients

Background: Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine carcinoma of the skin. Aim: To describe clinical outcome and prognostic factors of MCC patients in two expert-centers. Method: Patients with histologically confirmed MCC in 1990-2014 were included. Data on patient, tumor characteristics and treatment were retrospectively collected. Results: A total of 351 Patients were evaluated, 153 (44%) males, median age 74 years (range 28-94). Median follow-up time was 28 months (IQR 13-58). Median primary tumor size was 17 mm (range 2-135). At time of diagnosis 112 (32%) patients had lymph node metastases. The cohorts′ 5-year overall survival (OS) was 58%. Using a competing risk analysis the 5-year relapse and MCC related death was 42% and 22%. Adjuvant radiation therapy (XRT) was associated with reduced recurrence (SDH 0.54; CI 0.3-0.9). Nodal involvement (SDH 2.7; CI 1.1-6.6) and the male gender were associated with higher MCC related death (SDH 3.1; CI 1.2-7.9). Conclusion: In a large cohort a low MCC related death, in the presence of a low OS was seen. This indicates that a significant number of MCC patients die due to other causes than MCC. Adjuvant XRT was associated with relapse. Male gender and nodal metastasis were associated with MCC related death.