Koselugo (selumetinib) has been approved in Japan for the treatment of paediatric patients three years of age and older with plexiform neurofibromas (PNs) in neurofibromatosis type 1 (NF1) with clinical symptoms, such as pain and disfigurement, and PNs which cannot be completely removed by surgery without risk of substantial morbidity.1 The approval by the Japanese Ministry of Health, Labour and Welfare (MHLW) is based on positive results from the SPRINT Stratum 1 Phase II trial sponsored by the National Institutes of Health's National Cancer Institute (NCI) Cancer Therapy Evaluation Program (CTEP). The trial showed Koselugo, an oral treatment option, reduced the size of inoperable tumours in children.1,2 Additionally, a Phase I trial in Japanese paediatric NF1 patients with symptomatic and inoperable PNs was also evaluated as a basis for the approval, with the trial showing tumour reduction. The SPRINT Stratum 1 Phase II trial showed Koselugo demonstrated an objective response rate (ORR) of 66% (33 of 50 patients, confirmed partial responses) in paediatric patients with PNs in NF1 when treated with Koselugo as twice-daily oral monotherapy.1 ORR is defined as the percentage of patients with confirmed complete (disappearance of PNs) or partial response (at least 20% reduction in tumour volume).1 The most common adverse reactions in the SPRINT trial were vomiting, blood creatine phosphokinase increase, diarrhoea and nausea.1 Results from the SPRINT Stratum 1 Phase II trial were published online in The New England Journal of Medicine.2 In addition to Japan, Koselugo is also approved in the US and EU for the treatment of paediatric patients with NF1 and symptomatic, inoperable PNs. Further regulatory submissions are underway.