Is adjuvant treatment for melanoma in clinical practice comparable to trials? The first population-based results.

e21523 Background: Little is known about the outcome of adjuvant therapy in melanoma patients beyond the clinical trial setting. The Dutch Melanoma treatment Registry (DMTR) is a population-based registry, set up in July 2013 to monitor the safety and quality of melanoma care. Since 2019, adjuvant treated melanoma patients have also been registered in the DMTR, following approval and reimbursement of adjuvant treatment in the Netherlands in December 2018. Methods: Analyses were performed on melanoma patients treated with adjuvant anti-PD1 therapy included in the DMTR between 01-07-2018 and 31-12-2019. Descriptive statistics were used to analyze patient-, and treatment characteristics, and death as well as relapse rates. Results: Six hundred and fifty-seven patients treated with adjuvant systemic therapy were included in the DMTR. The majority (94%) of these patients was treated with anti-PD1. Twenty percent of the anti-PD1-treated patients developed grade ≥3 toxicity. Of the 279 patients with a minimum follow-up of one year after start of anti-PD1, 170 (61%) prematurely discontinued therapy. Relapse and death occurred in respectively, 38% and 12% of patients within one year of follow-up. Relapse was significantly more frequent in older patients, with high Breslow thickness and ulcerated melanomas. Conclusions: These data show more frequent premature discontinuation of adjuvant anti-PD1 in daily clinical practice than reported in the registration trials. Moreover, incidence of severe toxicity, relapse and death during adjuvant treatment appears higher in the real-world setting.