Successful treatment of lipofibromatosis-like neural tumor of the lumbar spine with an NTRK-fusion inhibitor.

Background: Lipofibromatosis-like neural tumors (LPF-NT) are a newly identified class of rare mesenchymal neoplasms. Current standard of care therapy is surgical resection alone; there are no chemotherapies or molecular targeted therapies that have been shown to be effective in patients who are not surgical candidates due to either tumor bulk or location. Most LPF-NT harbor NTRK fusions, although the therapeutic significance of these fusions has not been previously demonstrated in this malignancy. Here, we present the first case of a patient with surgically-unresectable LPF-NT successfully treated with medical therapy, specifically the TRK fusion-protein inhibitor entrectinib.

Case presentation: The patient is a 21 year old man with no co-morbidities who presented for evaluation due to intermittent abdominal pain and was found to have a mass spanning from T12-L2. Biopsy revealed a mesenchymal spindle cell neoplasm and S100 positivity pointed to possible nerve sheath origin. The sample was ultimately found to have an LMNA-NTRK1 fusion, confirming the diagnosis of LP-NFT. Unfortunately, due to the bulk and location of the tumor, surgery was felt to be exceptionally morbid and the patient was treated in a clinical trial with the NTRK inhibitor entrectinib. Surprisingly, he had such a robust clinical response that he was ultimately deemed a surgical candidate and he was successfully taken to surgery. Post-operative pathology revealed > 95% necrosis, demonstrating exceptional sensitivity to the targeted therapy. The patient remains NED and on entrectinib 12 months post-operatively.

Conclusions: The exceptional treatment response of this patient suggests that NTRK fusions are true drivers of the disease. Thus, all patients should be evaluated for NTRK fusions using sensitive methodologies and treatment with TRK fusion-protein inhibitors should be considered in patients who are not candidates for oncologic resection.