Molecular Characterization of Hotspot Mutations in HER2, BRAF, KRAS, and PIK3CA in Canine Pulmonary Adenocarcinoma from Japan.

Primary pulmonary adenocarcinoma in dogs is rare, and effective systemic therapies remain limited. To evaluate the molecular basis of potential precision oncology approaches, hotspot mutations in HER2, BRAF, KRAS, and PIK3CA were analyzed in 20 surgically resected canine pulmonary adenocarcinomas and three canine pulmonary adenocarcinoma cell lines. HER2 V659E and BRAF V595E mutations were each detected in 3/20 cases (15%), while KRAS G12V was detected in 1/20 cases (5%). No PIK3CA hotspot mutations were identified. The BRAF V595E mutation was additionally detected in the AZACL2 cell line. Functional analysis demonstrated increased sensitivity of AZACL2 cells to the BRAF inhibitor dabrafenib and MEK inhibitors including trametinib, compared with BRAF wild-type cell lines. These findings support MAPK pathway dependency in BRAF-mutant canine pulmonary adenocarcinoma. The mutation spectrum was broadly consistent with previous reports, suggesting a conserved molecular landscape across geographic regions. Collectively, these data identify BRAF and HER2 alterations as clinically relevant candidates for molecular diagnostics and targeted therapy in canine pulmonary adenocarcinoma.