Hotspot mutations in the spliceosome gene SF3B1 are reported in ∼20% of uveal melanomas.,SF3B1 is involved in 3′-splice site (3′ss) recognition during RNA splicing; however, the molecular mechanisms of its mutation have remained unclear.,Here we show, using RNA-Seq analyses of uveal melanoma, that the SF3B1R625/K666 mutation results in deregulated splicing at a subset of junctions, mostly by the use of alternative 3′ss.,Modelling the differential junctions in SF3B1WT and SF3B1R625/K666 cell lines demonstrates that the deregulated splice pattern strictly depends on SF3B1 status and on the 3’ss-sequence context.,SF3B1WT knockdown or overexpression do not reproduce the SF3B1R625/K666 splice pattern, qualifying SF3B1R625/K666 as change-of-function mutants.,Mutagenesis of predicted branchpoints reveals that the SF3B1R625/K666-promoted splice pattern is a direct result of alternative branchpoint usage.,Altogether, this study provides a better understanding of the mechanisms underlying splicing alterations induced by mutant SF3B1 in cancer, and reveals a role for alternative branchpoints in disease.,Mutations in the splicing factor SF3B1 are found in uveal melanoma.,Here, Alsafadi et al. use RNA-sequencing data from these cancers and experimental models, and show that mutant SF3B1 promotes alternative branchpoints in a specific gene subset and that the mutant protein gains a new function.
Ipilimumab improves survival in patients with advanced melanoma.,The activity and safety of ipilimumab outside of a clinical trial was assessed in an expanded access programme (EAP).,Ipilimumab was available upon physician request for patients aged 16 or over with pretreated stage III (unresectable)/IV melanoma, for whom no other therapeutic option was available.,Patients received ipilimumab 3 mg/kg every 3 weeks for four doses.,Patients with stable disease or an objective response to ipilimumab were eligible for retreatment upon disease progression.,Tumour assessments were conducted at baseline and week 12.,Patients were monitored for adverse events (AEs) within 3 to 4 days of each scheduled visit.,Of 855 patients participating in the EAP in Italy, 833 were evaluable for response.,Of these, 13% had an objective immune response, and the immune-related disease control rate was 34%.,Median progression-free survival and overall survival were 3.7 and 7.2 months, respectively.,Efficacy was independent of BRAF and NRAS mutational status.,Overall, 33% of patients reported an immune-related AE (irAE).,The frequency of irAEs was not associated with response to ipilimumab.,Outside of a clinical trial setting, ipilimumab is a feasible treatment option in patients with pretreated metastatic melanoma, regardless of BRAF and NRAS mutational status.,Data from this large cohort of patients support clinical trial evidence that ipilimumab can induce durable disease control and long-term survival in patients who have failed to respond to prior treatment.