BACKGROUND: The role of adjuvant immunotherapy (IO) in the treatment of Merkel cell carcinoma (MCC) is currently being explored in clinical trials. Here we aim to evaluate the real-world impact of adjuvant IO on survival in patients with MCC. METHODS: A retrospective analysis of the National Cancer Database was performed to identify patients with stage I-III MCC. Our main predictor of interest was IO in an adjuvant setting, stratified by receipt of radiotherapy (RT). A multivariable Cox proportional hazards regression model with inverse probability treatment weighting was used to estimate overall survival. RESULTS: A total of 353 patients received adjuvant IO, while 5,340 underwent surgery without adjuvant therapy. Among patients who received adjuvant IO, 10.2% had stage I disease, 7.1% stage II, and 82.7% stage III. Overall, adjuvant IO was not associated with a difference in survival (hazard ratio HR, 1.04; 95% CI, 0.86-1.26). Stratified analyses by stage demonstrated similar findings (stage I: HR, 1.4; 95% CI, 0.79-2.50; stage II: HR, 1.45; 95% CI, 0.67-3.13; stage III: HR, 0.98; 95% CI, 0.79-1.20). However, when an interaction term with RT was introduced with adjuvant IO, both treatments were associated with improved survival compared with surgery alone (HR, 0.53; 95% CI, 0.28-0.99), whereas adjuvant IO without RT was not associated with a significant survival difference (HR, 1.14; 95% CI, 0.83-1.60). CONCLUSIONS: The association between adjuvant IO on survival may be modified by RT, which should be considered when interpreting current adjuvant IO trials in MCC.
Morocho et al. (Tue,) studied this question.