The goal of this observational study is to describe the safety and effectiveness of larotrectinib in patients with locally advanced or metastatic TRK fusion cancer for whom a decision to treat with larotrectinib has been made before enrollment. This study will enroll participants with any tumors harboring the NTRK gene fusion including Soft Tissue Sarcomas, Central Nervous System, Melanoma, and Thyroid cancers.