Brain metastases in adult patients with melanoma of unknown primary in the Netherlands (2011–2020)

Background: Although patients with melanoma of unknown primary (MUP) have a better prognosis than similar-staged melanoma patients with known primary, the occurrence of brain metastases (BM) entails a serious complication. This study provides an overview of the incidence, treatment patterns, and overall survival (OS) of adult patients with BM-MUP in the Netherlands. Methods: BM-MUP cases were retrieved from the Netherlands Cancer Registry. Patient, disease and treatment-related characteristics were summarised using descriptive statistics. Overall survival (OS) was calculated by the Kaplan–Meier method, and the impact of prognostic factors on OS was assessed using Cox proportional hazard regression analyses. Results: Among 1779 MUP patients, 450 were identified as BM-MUP (25.3%). Of these patients, 381 (84.7%) presented with BM along with other metastases, while 69 (15.3%) had BM only. BM-MUP patients were predominantly male (68.2%), and had a median age of 64 years at diagnosis (interquartile range 54–71 years). Over time, the proportion of BM along other metastatic sites increased, and the occurrence of BM decreased (p = 0.01). 1-Year OS improved for the total population, from 30.0% (95% confidence interval (CI): 19.8–40.9%) in 2011–2012 to 43.6% (95%CI: 34.5–52.3%) in 2019–2020, and median OS more than doubled from 4.2 months (95%CI: 3.3–6.2 months) to 9.8 months (95%CI: 7.0–13.2 months). Patient’s age, localisation of BM, presence of synchronous liver metastasis and treatment were identified as independent predictors of OS. Conclusion: Notwithstanding the progress made in OS for patients with BM-MUP in the past decade, their overall prognosis remains poor, and further efforts are needed to improve outcomes.