TRK (TRKA/TRKB/TRKC, encoded by NTRK1/NTRK2/NTRK3 gene fusions)

Class

TRK tyrosine kinase inhibitor (FDA-approved, tumor-agnostic)

Pathway

blocks constitutively active TRK fusion proteins that drive oncogenic signaling regardless of tumor type

TRK refers to a family of three receptor tyrosine kinases—TRKA, TRKB, and TRKC—encoded by the genes NTRK1, NTRK2, and NTRK3. Normally, these receptors sit on the cell surface and are activated when neurotrophins, a class of growth factors, bind to them, triggering intracellular signaling that supports neuronal development, survival, and pain sensation. In certain cancers, chromosomal rearrangements fuse part of an NTRK gene to an unrelated gene, producing an abnormal fusion protein. This fusion protein activates the kinase continuously, without needing a neurotrophin signal, driving uncontrolled cell proliferation. Because this activating fusion can arise in many different tumor types—rather than being confined to one organ—the rationale for treatment is defined by the molecular alteration itself rather than by where the tumor originates, giving rise to tumor-agnostic drug development. TRK inhibitors are small molecules that occupy the kinase's active site, blocking its ability to transmit growth signals downstream. This mechanism matters broadly across oncology because it exemplifies a shift toward targeting shared genetic drivers rather than tissue of origin, offering a treatment rationale applicable wherever an NTRK fusion is identified, regardless of the underlying cancer type.