NTRK3 and nervous system cancer: Drug resistance was attributed to this mutation given previous demonstrations by others that the NTRK3 G623R mutation results in a steric inhibition between the arginine side chain of mutant TRKC and the hydroxypyrrolidine group of larotrectinib.11–12 The other patient in their report was a 4-year-old boy who had a 4 cm lipofibromatosis-like neural tumor of the mandibular bone and soft tissue.