The precision oncology approach to the treatment of cancer bases treatment decisions on the biology of an individual’s cancer, most often using genetic alterations or mutations to inform therapy. This approach has been successful in a few cancer types, including lung cancer, melanoma, and chronic myelogenous leukemia where oral targeted therapies have led to both improved patient outcomes and fewer side effects compared to standard chemotherapy. However, this approach has not yet realized its full potential in these or other cancer types. In this proposal we plan to study new cancer-causing gene mutations involving the NTRK1, NTRK2 and NTRK3 genes, which are found in numerous types of cancer. We have already demonstrated that tumor cells treated with targeted therapies against this gene family can kill cancer cells in the laboratory. We have also observed early and dramatic tumor shrinkage in patients with different tumor types that share mutations in these NTRK genes. This proposal will focus on determining additional mutations of NTRK genes that may respond to therapy. The proposal will also study how cancer cells become resistant to targeted therapies and develop new laboratory models of NTRK+ cancer to develop new therapies for these cancers.