Case-control study of survival impact of adjuvant radiotherapy after surgical resection of stage III Merkel cell carcinoma

Adjuvant radiotherapy (aRT) to the primary tumor site is associated with reduced recurrence and improved survival in stage I and II Merkel cell carcinoma (MCC). Its utility in stage III MCC remains a controversial topic. A case-control study using the National Cancer Database (2004-2016) identified 2683 surgically resected stage III MCC patients (67.1% receiving aRT; 17.8% receiving additional RT to their lymph node basin). Propensity score matching of patients who did or did not receive aRT identified 1756 patients. Median overall survival among patients who received aRT was 60.6 months (range 46.6-74.5), while median OS among patients not receiving aRT was 38.7 months (range 33.7-43.8), a statistically significant difference (p<0.001). Subgroup analysis after PSM of patients with aRT to their LN basis revealed no survival benefit. The authors conclude that among patients with resected stage III MCC, aRT resulted in improved OS. The lack of clear consensus for the role of aRT in stage III MCC is likely due to a heterogeneous population in prior studies.