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Larotrectinib for Pediatric Undifferentiated Sarcoma With an STRN-NTRK2 Fusion: Case Study

By: Vanessa A. Carter, BS
Posted: Tuesday, August 10, 2021

Theodore W. Laetsch, MD, of The University of Texas Southwestern Medical Center, Dallas, and colleagues presented a case of undifferentiated sarcoma with an STRN-NTRK2 fusion that achieved a “profound and durable clinical response” on larotrectinib treatment, in JCO Precision Oncology. These findings demonstrate that genomic testing is becoming more useful in identifying therapeutic targets, and the authors suggest it should be offered to all individuals with aggressive cancer.

An 11-year-old girl presented with leg and back pain for 1 month. A 9.6 × 7.4-cm unresectable mass was discovered surrounding the aorta and affecting the vertebral bodies. A diagnosis of nonrhabdomyosarcoma soft-tissue sarcoma was determined by biopsy, but it was later revised to undifferentiated sarcoma. The patient was administered neoadjuvant chemotherapy followed by ifosfamide and etoposide.

Disease progression continued after two chemotherapy cycles, despite the administration of sorafenib. Therefore, the patient underwent exploratory laparotomy with reconstruction and resection of the abdominal aorta, tumor resection, resection of the sigmoid colon with end colostomy, placement of bilateral ureteral stents, and ligation and resection of the inferior vena cava.

Pulmonary metastasis, PET-avid tumors, and malignant massive ascites were identified. Since her condition did not improve, next-generation sequencing was performed, revealing an STRN-NTRK2 fusion. The patient was then enrolled in the phase I trial of larotrecinib 2 months after surgery, receiving the TRK inhibitor twice a day.

Just 14 days after treatment began, the patient’s back pain and ascites had resolved, and she was less fatigued. Resolution of PET avidity in all tumors as well as significant reduction in tumor size and pulmonary metastases were observed after cycle 1. After 5 months, the patient had her Denver shunt removed and her colostomy was closed.

Larotrectinib was reported to be well tolerated, with grade 1 fatigue and grade 1 to 2 cytopenias being the sole treatment-related adverse events. After 22 months on larotrectinib, there was residual PET-negative tissue at the tumor invasion site, with complete resolution of pulmonary metastasis.

Disclosure: For full disclosures of the authors, visit ascopubs.org.



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