A 6-year-old female presenting with an abdominal mass was found to have an unresectable undifferentiated sarcoma. The tumor did not respond to multiagent chemotherapy. However, molecular testing identified an NTRK3-fusion, and treatment was changed to larotrectinib monotherapy. Following 6 months of therapy, the patient achieved a very good partial response with 96% reduction in tumor size. She underwent proton beam radiation therapy with continued larotrectinib therapy and achieved a complete response. This case report shows that an NTRK fusion positive undifferentiated sarcoma can be safely treated with larotrectinib and radiation therapy and highlights the importance of early molecular testing.
Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.