Selumetinib Treatment in a Neurofibromatosis Type 1 Child With Second Hit Mutation on the NF1 Gene.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder, with plexiform neurofibromas occurring in approximately 20%-50% of patients. A 12-year-old girl underwent surgery due to unbearable pain caused by diffuse neurofibromas. Postoperatively, the girl exhibited rapid growth and extremely extensive plexiform neurofibromas, with multiple plexiform neurofibromas that were inoperable. Through high-throughput sequencing (HTS), genetic molecular analysis was conducted on the peripheral blood samples of the child, and it was found that there was a splice site mutation c.3113 + 1G > A in the NF1 gene. Additionally, we identified a pathogenic variant c.2033dup (Ile679Aspfs*21), citing ClinVar and PMID: 77655472 to confirm its established pathogenicity in the paraffin-embedded section sample of the diffuse neurofibroma, which was exclusively found in the girl's plexiform neurofibroma. This 'second-hit' mutation could explain the rapid growth of the diffuse neurofibroma. The patient was effectively treated with oral administration of the selective MEK inhibitor selumetinib, resulting in rapid tumour regression. The treatment has shown promising efficacy against the rapid tumour growth induced by the patient's 'second-hit' mutation.