not-yet-known not-yet-known not-yet-known unknown Larotrectinib Larotrectinib, also known as LOXO-101, is an orally administered inhibitor that targets TRKA, TRKB, and TRKC, with a 50% inhibitory concentration (IC50) of 5–11 nM in vitro, and its sensitivity for TRK exceeds 100 times over other kinases.(22) Larotrectinib has been shown to be clinically active in infants, children, adolescents adult patients with TRK fusion-positive cancers.(22–24) In this case, Larotrectinib allowed for a decrease in tumor size, and improvements of the symptoms. This case report demonstrates the potential of targeted therapies in selected pediatric patients with unique oncogenic drivers for which specific inhibitors are available. Our patient presented with back pain and lower limb weakness that improved after initiation of Larotrectinib in addition to dexamethasone. It is worth mentioning that there was a one-time deterioration following the discontinuation of Larotrectinib. In ½ phase clinical trial studying the use of Larotrectinib in pediatric NTRK fusion-positive solid tumors, patients received larotrectinib orally, either in capsule or liquid form, twice daily In 28-day cycles of continuous dosing. For patients with locally advanced sarcomas, surgical intervention was an option after achieving a satisfactory response to the treatment. Patients with no residual tumor at the resection margin (UICC-R0) were able to discontinue larotrectinib and undergo regular radiographic imaging every 3 months. Patients with marginal (R1) or gross residual (R2) surgery were eligible to resume larotrectinib immediately after the surgery. Patients who showed a positive response to larotrectinib were allowed to enter a ”wait and see” period, during which the drug was discontinued for a minimum of six treatment cycles. If disease progression occurred after drug discontinuation, retreatment with larotrectinib was possible.(23) In our case report, we followed the recommendation of phase ½ clinical trial for the dose of Larotrectinib which is 100mg maximum per dose, though, it was for ten months. The Larotrectinib started after five months of the last spinal tumor resection. On the other hand, several cases with NTRK-fusions demonstrated promising results in disease control with targeted therapy and long-term survival. Specifically, a number of LGGs cases showed clinical benefits evidenced by MRI. (19,20,25) Moreover, high efficacy in multiple NTRK-driven cancers is shown by the use of NTRK inhibitors (e.g. Larotrectinib).(26) Regarding the adverse events of Larotrectoinib, patients with solid tumors experienced various adverse events, including increased levels of liver enzymes (ALT or AST), fatigue, vomiting, dizziness, nausea, anemia, diarrhea, constipation, cough, weight gain, shortness of breath, headache, fever, joint pain, back pain, and decreased neutrophil count, thrombocytopenia, bleeding, and anemia.(10,22–24,27)