Adjuvant Larotrectinib in a Resected Secretory Carcinoma-Like Lung Adenocarcinoma Harboring EML4-NTRK3 Fusion: Case Report.

Secretory carcinoma of the lung is an exceptionally rare salivary gland-type malignancy, typically associated with NTRK fusions. We report a 71-year-old woman with pulmonary stage IIIA adenocarcinoma having salivary gland differentiation and solid-cribriform architecture, confirmed by S100 and Pan-TRK immunohistochemistry. Broad DNA and RNA next-generation sequencing identified an fusion. After adjuvant chemotherapy, maintenance larotrectinib was initiated based on proven TRK inhibitor efficacy in metastatic NTRK-fusion tumors and emerging evidence for targeted therapy benefit in driver-positive early stage lung adenocarcinoma. Our findings demonstrate the value of molecular pathology in the diagnostic journey of pulmonary malignancies, guiding rare fusion detection and supporting therapeutic decisions based on rare fusions in early stage disease.