NTRK1 and neoplasm: Moreover, in tumor samples from 10 patients, amino acid substitution of the kinase domain was observed involving the solvent front position (TrkA G595R or TrkC G623R), the gatekeeper position (TrkA F589L), and the xDFG position (TrkA G667S or TrkC G696A) which eliminates unfavorable interactions by preventing inhibitor binding.