NTRK1 and breast cancer: Fusion variations of neurotrophic receptor tyrosine kinase (NTRK) are oncogenic drivers in various solid tumors such as breast cancer, salivary gland carcinoma, infant fibrosarcoma, etc. Gene rearrangements involving NTRK1/2/3 lead to constitutive activation of the tropomyosin receptor kinase (TRK) domain, and the expressed fusion proteins drive tumor growth and survival.