Trametinib for multiple non-ossifying fibromas due to KRAS mosaic mutations: two case reports.

BACKGROUND

KRAS mosaic activating variants are the main cause of non-ossifying fibromas (NOFs), the most common benign lesion of the growing skeleton. Multifocal NOFs cause bone fragility, and no specific treatment is currently available.

METHODS

We report two children, carrying mosaic KRAS variants (p.G13D and p.A146T), presenting with oculoectodermal syndrome and recurrent fractures due to progressive polyostotic NOFs. To assess the impact of these mutations on KRAS function, we conducted transient KRAS overexpression in HEK293 cells and then tested the effect of the MEK-inhibitor trametinib at the cellular level.

RESULTS

We show that trametinib yields, in vitro, significant reduction of RAS-pathway hyperactivation induced by the two KRAS variants and, in vivo, remarkable clinical and radiological improvement with no recurrence of fractures and reossification of NOFs under treatment; resurgence of lesions is observed one year after stopping treatment.

CONCLUSIONS

Hence, trametinib constitutes a promising precision therapeutic approach for severe KRAS-related NOFs.