399 Feasibility of BRAF VE1 Immunohistochemistry in Pulmonary Pathology

Introduction/Objective The BRAF VE1 immunohistochemical (IHC) stain can recognize BRAF V600E-mutant proteins and coincidently highlights cilia due to cross-reactivity of the antibody with epitopes in axonemal dyneins. This phenomenon has not been extensively studied. Our aim was to therefore investigate the utility of BRAF IHC staining in pulmonary tissue. Methods/Case Report Archival cases where BRAF IHC was performed on pulmonary tissue were retrieved. Clinical and pathological findings were recorded and IHC slides reviewed. Results BRAF IHC was available for 49 thoracic specimens including 26 biopsies, 22 surgical resections and 1 cytopathology cell block case. BRAF staining highlighted cilia at the apical surface of bronchial cells in 39 cases (80%). Cytoplasmic or nuclear staining was considered abnormal, with artifactual staining seen in 18 cases (e.g. histiocytes, mucin). Unexpected, non-apical staining in 10 slides occurred with adenocarcinoma (3 of 14 adenocarcinomas in the cohort), thoracic sialadenoma papilliferum, atypical adenomatous hyperplasia, benign cartilage, and vessels. BRAF failed to stain two entirely benign cases (one with scar tissue). Conclusion BRAF IHC is an underutilized ancillary tool in thoracic pathology. By highlighting the presence of cilia, BRAF has potential in most cases to distinguish benign from malignant pulmonary tissue.