Selitrectinib is primarily used in the field of oncology as a targeted therapy for cancers that involve specific genetic mutations. It is designed to inhibit tropomyosin receptor kinase (TRK) fusion proteins, which are often implicated in the growth and spread of certain tumors. This makes it particularly effective in treating cancers such as TRK fusion-positive solid tumors, including those found in the lung, thyroid, and soft tissues. By blocking the activity of these proteins, selitrectinib helps to slow down or stop the progression of cancer, offering a therapeutic option for patients who may not respond to conventional treatments. Its application is often considered in cases where other TRK inhibitors have failed, providing a potential alternative for managing resistant forms of cancer.