LAUSR

e18641 Background: The introduction of new systemic treatments for advanced melanoma has markedly changed the outcome of patients with metastatic melanoma. To assure high quality of care for patients treated in Dutch melanoma centers, hospital variation in treatment patterns and outcomes are evaluated in the Dutch Melanoma Treatment Registry. The aim of this study was to assess center variation in treatments and 2-year survival probabilities of patients diagnosed between 2013-2017 in the Netherlands. Methods: We selected patients diagnosed between 2013-2017 with unresectable stage IIIC or IV melanoma, registered in the Dutch Melanoma Treatment Registry. Centers’ performance on 2-year survival was compared by means of a multivariable Cox proportional hazards model with a random effect for center ID. Variation between centers was expressed by median hazard ratios. Therapy with BRAF/MEK inhibitors, anti-PD-1 antibodies or ipilimumab plus nivolumab was added to the Cox proportional hazards model as a time dependent covariate to assess the influence of new systemic therapies on center variation. Results: Between 2013-2017, 3820 patients were diagnosed with unresectable stage IIIC or IV melanoma. For patients diagnosed between 2013-2015, significant center variation in 2-year survival probabilities was observed. Median hazard ratio was 1.17 (95%CI: 1.09-1.31) for patients diagnosed between 2013-2015 after correcting for case-mix and treatment with BRAF/MEK inhibitors, anti-PD-1 antibodies or ipilimumab plus nivolumab. Use of new systemic therapies had a significant effect on up to 2-year survival (hazard ratio = 0.83, 95%CI (0.73-0.94)) with no use of the new systemic therapies as a reference. From 2016 onwards, no significant difference in 2-years survival was observed between centers. Conclusions: The different use of new cancer treatment of metastatic melanoma had an effect on survival outcomes in the Netherlands. A platform such as the Dutch Melanoma Treatment Registry, in which melanoma centers collaborate and have insight in variation in treatment patterns and outcomes between centers, results in fast implementation of new clinical developments across all Dutch melanoma centers.