Background: Mucosal melanoma is rare and associated with extremely poor prognosis. There was no standard treatment for advanced mucosal melanoma patients. BEAM study had demonstrated the effectivity and safety of bevacizumab combined with carboplatin plus paclitaxel in patients with previously untreated metastatic melanoma. This study was to evaluate the activity of bevacizumab combined with carboplatin plus paclitaxel in Patients with Previously Untreated Advanced Mucosal Melanoma. Methods: This study is an open-label, multicenter, randomized phase II trial. Eligible patients had metastatic, recurrent, or unresectable mucosal melanoma and no received any systemic therapy before enrollment. Patients were randomly allocated in a 2:1 ratio to receive bevacizumab (CPB arm, 5mg/kg every two weeks) or placebo (CP arm) with carboplatin (area under the curve, 5) plus paclitaxel (175 mg/m²). Treatment was continued for both groups until disease progression, unacceptable toxicity, death, or withdrawal of consent. The primary study endpoint is progress-free survival (PFS). Overall survival, disease control rate, and safety will also be assessed. Results: The first patient visit was December 1st, 2013, and the final data cutoff was August 30th, 2018. At that time, 114 patients were randomly assigned to receive CP or CPB therapy. Median PFS was 3.2 months for the CP arm and 4.7 months for the CPB arm (HR, 0.50; 95% CI, 0.33-0.72; P = 0.001). Median OS was 9.0 months in the CP arm versus 12.9 months in the CPB arm (HR, 0.61; 95% CI, 0.40-0.92; P = 0.02). The PFS was longer in the CPB arm in the subgroups of patients with neutrophil-to-lymphocyte ratio (NLR) more than 4 and patients with abnormal lactate dehydrogenase concentration (1.2 v 3.0 months, HR, 0.38; 2.0 v 4.7 months, HR, 0.39, respectively). Multivariate analysis using the Cox model showed that combination with bevacizumab was the predictor for better disease control and survival (PFS: HR 0.400, 95% CI 0.251-0.636, P < 0.001; OS: HR 0.505, 95% CI 0.313-0.814, P = 0.005). No new safety signals were observed. Conclusions: To our knowledge this is the largest study about advanced mucosal melanoma. This study demonstrated that bevacizumab in combination with carboplatin plus paclitaxel is active and safe regimen as first line treatment in patients with in advanced mucosal melanoma. A phase III study will be necessary to confirm the benefit, especially in some special setting such as elevated NLR and elevated LDH subgroups. Clinical trial information: NCT02023710