Survival analysis of metastatic Merkel cell carcinoma patients pre- and post-immunotherapy era in the US: A retrospective population-based study.

e21515 Background: In 2017, the U.S. Food and Drug Administration (FDA) approved the first immunotherapy (avelumab) to treat metastatic Merkel cell carcinoma (MCC). This study explores survival analysis before and after the immunotherapy era in MCC patients. Methods: Data of patients with MCC was extracted from 2000 – 2021 using the Surveillance, Epidemiology, and End Results database (SEER). Patients were divided into two groups the pre-immunotherapy cohort (2000-2016) and the post-immunotherapy cohort (2017-2021). Results: Data from 10,481 patients were obtained from the SEER database. Most patients were 70 years of age and greater (69%), male (63%), and white (90%). Age, gender, tumor size, chemotherapy, radiation, and surgery were significant predictors of 1-, 3-, and 5-year cancer-specific survival (CSS) and overall survival (OS). Among these, age at diagnosis and tumor size were the most influential factors in the predictive nomograms for both OS and CSS. For patients at the M1 stage, the 5-year OS rate increased from 2.4% (95% CI: 1.3–4.6) pre-immunotherapy to 63.2% (95% CI: 44.8–89) post-immunotherapy era. Similarly, for those at both M1 and N1 stages, the 5-year OS rate rose from 5.5% (95% CI: 4.3–7.0) pre-immunotherapy to 61.2% (95% CI: 54.5–68.7) post-immunotherapy era. Across all patients, the 5-year OS rate increased from 15.4% (95% CI: 14.3–16.5) pre-immunotherapy to 29.6% (95% CI: 27.8–31.6) post-immunotherapy era. With regards to the survival site, the skin of the upper limb and shoulder had the highest survival rate while the skin of the scalp and neck region had the lowest survival (p < 0.0001). Conclusions: There was a significant increase in survival in patients with metastatic MCC in the post-immunotherapy era.These findings underscore the potential of immunotherapy drugs like avelumab in enhancing survival prospects and suggest that further research should explore optimizing treatment strategies based on these factors.