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Gregory J. Riely, MD, PhD


NTRK3 Fusion–Positive Sarcoma: 6-Year-Old Girl Treated With Larotrectinib and Radiotherapy

By: Vanessa A. Carter, BS
Posted: Thursday, June 23, 2022

Kenneth B. DeSantes, MD, of Carbone Cancer Center, Madison, Wisconsin, and colleagues presented a pediatric case of undifferentiated and unresectable sarcoma harboring an NTRK3 fusion. Published in the Journal of Pediatric Hematology/Oncology, this case study featured a successful treatment regimen of the TRK inhibitor larotrectinib plus proton beam radiotherapy.

A previously healthy 6-year-old female presented with a 6-month history of abdominal pain, decreased appetite with early satiety, weight loss, and intermittent nausea. Upon physical examination and abdominal ultrasound, a hypervascular mass was identified; it extended from the pelvic brim to the umbilicus. Metabolic panels appeared normal, although urinalysis showed ketones, protein, and amorphous crystals.

Computed tomography (CT) scans confirmed an 11-cm heterogeneous mass with invasion of the anterior L4 and L5 vertebral bodies; metastatic disease was not detected. The mass was deemed unresectable, but biopsy revealed pathology suggestive of Ewing-like sarcoma. The patient was administered vincristine, doxorubicin, and cyclophosphamide but experienced disease progression. Tumor tissue was sent for immunostaining and was revealed to be positive for pan-NTRK, with an NTRK3 gene arrangement. Therefore, the patient was given larotrectinib monotherapy.

After 3 months of therapy, a CT scan demonstrated a very good partial response, with a 95% decrease in tumor size. Significant shrinkage remained after 6 months of therapy, and local tumor control was initiated with proton beam radiation with continuation of larotrectinib during therapy. Approximately 3 months after completing radiotherapy, a repeat CT scan showed further tumor reduction; after an additional 3 months, the mass was unchanged and was thought to be residual scar tissue.

Larotrectinib monotherapy was continued for 12 months following the completion of proton beam radiation therapy, for a total of 22 months of treatment. The patient remains in remission 9 months after completing treatment.

Disclosure: One of the study authors received honoraria for serving as an advisor to Nektar Therapeutics and Novartis. The other study authors reported no conflicts of interest.

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