The effect of time to postoperative radiation therapy on survival in resected merkel cell carcinoma

Objectives: Delays from surgery to adjuvant radiation therapy (aRT) are associated with poorer prognosis in multiple neoplasms. Presently, no data exist for Merkel cell carcinoma (MCC). The authors sought to assess the time interval from surgery to aRT and effect on outcomes in MCC. Materials and Methods: The National Cancer Database was queried for histologically confirmed nonmetastatic MCC status post resection and aRT diagnosed between 2004 and 2015 who received aRT within 24 weeks of surgery. Kaplan-Meier analysis assessed univariate overall survival (OS); multivariable Cox proportional hazards modeling assessed multivariate OS; χ² and logistic regression assessed differences in baseline characteristics and predictors of delayed aRT. Results: Of 5952 patients meeting criteria, 13% commenced aRT within 4 weeks, 48% between 4 and 7 weeks, 23% between 8 and 11 weeks, 11% between 12 and 15 weeks, and 6% between 16 and 24 weeks. There were no differences in OS on the basis of the surgery-aRT interval (P=0.99). Predictors of worse OS on the multivariate analysis included advanced age, greater comorbidities, male sex, lower regional income, earlier year of diagnosis, more advanced tumor and nodal staging, positive margins, head and neck location, and treatment at community facilities (P<0.05 for all). Factors predictive of delayed aRT were identified. Subset analyses on these factors, such as receipt of chemotherapy or positive lymph nodes, did not demonstrate that the timing of aRT affected survival (P≥0.37). Conclusion: This study of a contemporary national database revealed that delays from resection to aRT were not associated with survival in MCC, somewhat discordant from other malignancies such as squamous cell carcinoma.