Respiratory function in children and young adults affected by neurofibromatosis type 1 treated with selumetinib

Background: Plexiform neurofibromas (PNs) are benign tumors that can cause pain, disfigurement, and disability in patients with neurofibromatosis type 1. Selumetinib, a MEK1/2 inhibitor, is the first drug who showed efficacy in inducing PNs shrinkage, reducing the associated morbidities in pediatric patients. Overall, selumetinib showed a good safety profile. However, multiple adverse effects have been reported both in pediatric and adult patients, including respiratory ones. Serial spirometry is suggested in patients with thoracic neurofibromas to detect changes that may underly PN's modifications. The aims of this study are to investigate the trend of pulmonary function in pediatric patients with NF1 treated with selumetinib and to determine the onset of respiratory adverse events. Methods: This is a retrospective study conducted at the Pediatric Department of the Institute for Maternal and Child Health IRCCS "Burlo Garofolo" in Trieste, Italy. We identified all the patients diagnosed with NF1 at our institution who received selumetinib. We excluded patients unable to perform spirometry at treatment start, and patients above 18 years of age. We registered patients' forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1) for the first two years of follow-up and record any possible respiratory adverse effect since the beginning of the treatment. Results: A total of 21 patients were included (7 females, 14 males) out of the 24 treated with selumetinib. Patients' median age when selumetinib was started was 12 years. Neurofibromas were located mostly in the upper body, but 13 of them were in the thoracic area. The duration of the clinical follow-up ranged from 9 months to 72 months (6 years), with a mean follow-up length of 37 months. During the follow-up period, none of the patients reported pulmonary symptoms and no significant changes of the spirometry values were detected. Among those with thoracic plexiform neurofibromas, no correlation was found between spirometry values and PN's volumetric changes at the MRI. Conclusions: Our experience suggests that selumetinib does not impact on pulmonary function in children and young adults. Serial spirometry should not be mandatory or could be at least distanced since it is not an appropriate method to precisely monitor plexiform neurofibromas changes over time.