NTRK3 and cancer: Recurrent NTRK gene fusions involving ETV6 and NTRK3 (Fig. 2b) were first identified in infantile (or congenital) fibrosarcoma, a malignant tumor of fibroblasts that occur in patients aged 2 years or younger [11], and then shortly after in congenital mesoblastic nephroma, the renal counterpart of infantile fibrosarcoma [12, 13].