NTRK1 and mesenchymal cell neoplasm: Although reciprocal translocations resulting in the canonical ETV6::NTRK3 fusion have been well recognized as the leading driver of infantile fibrosarcoma [19], the emerging group of mesenchymal tumors characterized by intra-chromosomal events at the NTRK1 1q23 locus (unbalanced interstitial deletions or cryptic inversions) have been only recently identified as a result of the wide application of RNA sequencing in clinical practice [6].