NTRK3 and fibrosarcoma: However, except for ETV6–NTRK3 fusion in congenital mesoblastic nephroma (cellular or mixed subtypes) and infantile fibrosarcomas with a prevalence of >90% in selected series of patients (20–23), the prevalence of NTRK fusion is found at much lower frequencies (5–25 or <5%) in other more common tumors such as breast, lung, and colorectal cancers.