1145P Clinical characteristics and survival of patients with advanced Merkel cell carcinoma (MCC) treated with avelumab: Analysis of a prospective German MCC registry (MCC TRIM)

MCC is a rare and aggressive form of skin cancer. Avelumab was the first immunotherapy approved for adult patients with metastatic MCC in Europe. We investigated the clinical characteristics and survival outcomes of patients with MCC at the start of and after avelumab treatment. Data from 684 patients in a prospective, noninterventional, multicenter, dynamic cohort of the MCC TRIM study who were enrolled after March 2019 were analyzed. Primary data from a study-specific electronic case report form and secondary data from the German national skin cancer registry ADOReg were combined. At data cutoff (Sept 30, 2022), patients diagnosed with unresectable stage III or IV MCC prior to avelumab treatment were included in this analysis. Survival outcomes were assessed by the Kaplan-Meier method. Of 116 patients with MCC receiving avelumab, 35.3% had stage III disease and 64.7% had stage IV. The mean (SD) age at initial diagnosis was 74.5 (10.4) y, and 62.1% of patients were male. Most patients had an Eastern Cooperative Oncology Group performance status ≤1 (76.7%); 21.6% had an immunosuppressive condition or took immunosuppressive medication. Diabetes was the most common comorbidity (23.3%). At a median follow-up of 28.75 mo (95% CI, 20.5-32.5 mo), median overall survival (OS) was not reached in stage III patients and was 52.0 mo (95% CI, 15.4 mo-not estimable [NE]) in stage IV patients. Median (95% CI) progression-free survival (PFS) was 11.8 mo (5.6 mo-NE) in stage III patients and 9.3 mo (3.5-13.7 mo) in stage IV patients. Most patients (86.2%) received avelumab as first-line (1L) therapy; of these, 37.0% had stage III disease and 63.0% had stage IV. Median OS with 1L avelumab was not reached in the stage III or IV group, but fewer events were observed in stage III vs stage IV patients (16.2% vs 36.5%); median PFS (95% CI) was 15.6 mo (5.6 mo-NE) and 7.3 mo (3.0-13.7 mo), respectively. Demographics observed in MCC TRIM reflect those of the typical advanced MCC population. This nationwide study indicates that avelumab is effective in stage III and IV patients with advanced MCC in routine clinical practice.