370 Changing incidence and presentation of merkel cell carcinoma in a retrospective single-center case series

Abstract

Merkel cell carcinoma (MCC) is an uncommon aggressive cutaneous neuroendocrine tumor with high mortality. The purpose of this study is to describe the pathologic characteristics and clinical correlates of MCC using a retrospective chart review of 117 cases in a single tertiary center pathology database from 1997 to 2015. MCC occurred mostly in the elderly (median age 76 years, range 22-99 years) and more often in males (M:F 1.21:1). MCC was most commonly located on the head and neck (n=59, 50%) followed by the upper extremities (n=16, 14%), lower extremities (n=13, 11%), and trunk (n=7, 6%). Males were more likely to have the tumor located on the trunk (relative risk [RR] 1.84, 95% confidence interval [CI] 1.26-2.68, p<0.01) and to also have a history of cutaneous squamous cell carcinoma (SCC) (RR 1.44, CI 1.04-1.99, p=0.03) when compared with females. A total of 55 cases (47%) exhibited metastasis with 75% (n=41) of these to the lymph nodes and 26% (n=14) to distant locations. MCC recurred in 17 cases (15%), with a median of 14 months to recurrence. Some common pathological characteristics of the primary skin tumor include lymphovascular invasion (n=21, 18%), necrosis (n=16, 14%), ulceration (n=10, 9%), and SCC collision (n=5, 3%) but these features did not correlate with outcome. Overall, there has been an increase in number of diagnoses per year from 1997 to 2015, with 2.3 times more cases diagnosed in the last 3 years of the study period than in the first 3 years. Cases diagnosed after 2006 were more likely to occur in younger patients, less than 76 years of age (RR 0.43, CI 0.24-0.78, p=0.01) and to occur in the upper extremities (RR 1.34, CI 0.996-1.80, p=0.05). Prior to 2006, the median age was 81 years, while after 2006, the median age decreased to 75 years. This retrospective case series elucidates MCC epidemiologic and pathologic characteristics, including how incidence, age at diagnosis, and location have changed over the course of the study.