Reduced Wide Local Excision Margins are Associated with Increased Risk of Relapse and Death from Merkel Cell Carcinoma

Introduction. Current recommendations regarding the size of wide local excision (WLE) margins for Merkel cell carcinoma (MCC) are not well established. Methods. WLE and pathologic margins were respectively reviewed from 79 patients with stage I or II MCC, who underwent WLE at Washington University in St Louis from 2005 to 2019. Outcomes included local recurrence-free survival (LRFS), regional recurrence-free survival (RRFS), distant recurrence-free survival (DRFS), disease-free survival (DFS), and disease-specific survival (DSS). Results. Thirty-two percent of patients received adjuvant radiotherapy (aRT). At 1 year, DFS was 51.3%, 71.4%, and 87.8% for patients with WLE margins < 1 cm, 1-1.9 cm, and >= 2 cm, respectively (p = 0.02). At 3 years, the DSS was 57.7%, 82.6%, and 100% for patients with WLE margins < 1 cm, 1-1.9 cm, and >= 2 cm, respectively (p = 0.02). Multivariable Cox analysis demonstrated that every 1-cm increase in WLE margins was associated with improved RRFS [hazard ratio (HR) = 0.28, 95% confidence interval (CI): 0.11-0.75], DRFS (HR 0.30, CI 0.08-0.99), DFS (HR 0.42, CI 0.21-0.86), and DSS (HR 0.16, CI 0.04-0.61). WLE and pathologic margin size were moderately-to-strongly correlated (r = 0.66). Close or positive pathologic margins (< 3 mm) were associated with reduced DRFS (HR 6.83, CI 1.80-25.9), DFS (HR 2.98, CI 1.31-6.75), and DSS (HR 3.52, CI 1.14-10.9). Conclusion. Reduced WLE and pathologic margins were associated with higher risk of relapse and death from MCC. Larger WLE margins are important in populations with lower rates of adjuvant radiation.