Survival Benefit of Guideline-Concordant Postoperative Radiation for Local Merkel Cell Carcinoma

Background: Postoperative radiation therapy (RT) for early-stage Merkel Cell Carcinoma (MCC) decreases the risk of locoregional recurrence and improve overall survival. However, concordance with RT guidelines is unknown. Materials and Methods: The National Cancer Database was queried for stage I/II MCC patients receiving surgical intervention from 2006-2017. The cohort was stratified by patients who had and did not have indication(s) for adjuvant RT of the primary tumor site based on National Comprehensive Cancer Network guidelines. We captured the use of RT, patient demographics, socioeconomic characteristics, and clinical characteristics. Logistic regression, Kaplan-Meier method, and propensity score weighted Cox proportional hazards model examined associations and survival benefits of RT. Results: 2,330 stage I/II MCC patients underwent surgical intervention. 1,858 (79.7%) met National Comprehensive Cancer Network criteria for RT of the primary tumor site, of which 1,062 (57.2%) received RT. 472 (20.3%) did not meet criteria for RT, of which 203 (43.0%) received RT. Five-year overall survival advantage was identified for patients who received RT when it was indicated (P < 0.003). There was no evidence of overall survival advantage when patients received guideline-discordant RT (P = 0.478). Conclusions: Surgical resection with adjuvant RT of the primary tumor site has an overall survival benefit for local MCC when patients meet criteria for RT. This study found a group who received guideline-discordant RT with no survival advantage. Further investigation is warranted to identify the socio-demographic and oncologic reasons for guideline discordance in the treatment of MCC for both under- and over-treatment.