Three locally invasive infantile fibrosarcoma cases treated with larotrectinib.

Background: Infantile fibrosarcoma is a rapidly growing soft tissue tumor, often managed by surgical resection, with chemotherapy and radiotherapy as additional options. Due to the high local aggressiveness and surgical morbidity, targeted therapies like larotrectinib can enhance quality of life and preserve organs, particularly in limb-threatening cases. Here, we present three cases where larotrectinib prevented mutilating surgeries.

Cases: The first patient presented antenatally with a 75 x 48 mm oral floor mass, severely narrowing the airway. Surgery was unfeasible due to invasion of vital organs, and complications arose with conventional chemotherapy. Following detection of an ETV6-NTRK3 fusion, larotrectinib was initiated, resulting in complete regression after two years. The second patient had a 42 x 37 mm right-hand tumor confirmed as infantile fibrosarcoma, for which initial treatment suggested amputation. After identifying an ETV6-NTRK3 fusion and failing to respond to chemotherapy, larotrectinib led to significant regression by year two, preserving hand function. The third patient presented with a 56 x 55 mm right foot mass at birth. Chemotherapy proved ineffective, and larotrectinib was initiated due to an ETV6-NTRK fusion signal, ultimately achieving near total regression within one year and avoiding amputation. All three cases demonstrated successful outcomes with targeted therapy.

Conclusions: These cases emphasize the importance of advanced molecular studies, like next-generation sequencing, for childhood tumors and integrating research with clinical trials. tropomyosin receptor kinase inhibitor larotrectinib may offer a safe and effective alternative to chemotherapy for NTRK fusion-positive, metastatic, or unresectable tumors.