Milestone discoveries that are relevant to normal TRK pathway biology (boxes above the timeline arrow) and NTRK fusions in cancer (boxes below the timeline arrow) are depicted. Key events relating to the following fields of study are colour coded as follows: neurotrophin identification (light blue), TRK function (red), TRK loss or NTRK-mutant phenotypes (yellow), TRK protein structure (green), TRK overexpression and splicing (grey), identification of NTRK fusions in clinical samples (orange), and clinical trials of TRK inhibitors (dark blue).