NFB-14. Post-operative use of MEK inhibitors to prevent rebound growth following partial resection of plexiform neurofibromas

Abstract

Abstract BACKGROUND: Plexiform neurofibromas (PNs) can cause significant morbidity leading to functional impairment, pain, and disfigurement. Management of PNs is challenging. Complete surgical resection is often not possible due to tumor growth along vital structures, and rebound growth is frequently experienced with partially resected PNs. The mitogen-activated protein kinase pathway has been implicated in the growth of PNs, and MEK1/2 inhibitors have been shown to be an effective treatment of PNs. OBJECTIVE: To describe our institutional experience using post-operative MEK1/2 inhibitors in the treatment of pediatric patients with PNs following subtotal resection (STR). METHODS: A single-institution retrospective record review. RESULTS: A total of 35 patients had STR of their PN. Fourteen patients underwent resection alone, ten patients received adjuvant mechanistic target of rapamycin (mTOR) inhibitors and eleven patients received adjuvant MEK1/2 inhibitors. The mean follow-up time was 5.1 years, but relatively shorter for patients receiving adjuvant MEK1/2 inhibitors. Mean time from resection to start of adjuvant therapy and mean duration of adjuvant therapy for patients in the mTOR inhibitor group was 3.3 weeks and 3.9 months, respectively, and for patients in the MEK1/2 inhibitor group was 3.1 weeks and 8.5 months, respectively. The number of patients in each group requiring additional treatment with surgical resection or medical therapy, was 11 of 14 patients (78.6%) in the resection only group, 7 of 10 patients (70%) in the adjuvant mTOR inhibitor group and 3 of 11 patients (27.3%) in the adjuvant MEK1/2 inhibitor group. CONCLUSIONS: A short course of MEK1/2 inhibitors following subtotal resection of PNs is effective in the short term in preventing rebound growth when compared to STR alone or adjuvant mTOR inhibitors. Treatment is well tolerated and should be considered as adjuvant therapy in pediatric patients. Long-term follow-up is necessary to judge the effectiveness of this approach.