Larotrectinib in NTRK3 fusion–positive metastatic secretory carcinoma of the breast: A case study

Triple-negative breast cancer (TNBC) is an aggressive heterogeneous form of breast cancer that accounts for 15 %-20 % of all breast cancers. Characterized by an absence of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expression, TNBCs are often treated with surgery, chemotherapy, radiation, and, most recently, with immunotherapy; however, patients with treatment-resistant TNBC often relapse and have an extremely poor prognosis. Here we present a case of recurrent metastatic TNBC responsive to the TRK inhibitor larotrectinib.