BRAFV600E in Papillary Thyroid Carcinoma Is Associated with Increased Programmed Death Ligand 1 Expression and Suppressive Immune Cell Infiltration

Background: There remain a small number of patients with papillary thyroid cancer (PTC) who suffer recurrence, metastases, or death. While mutation of the BRAF gene, corresponding to the constitutively active BRAFV600E protein, has been associated with worse clinical outcomes in thyroid cancer, the reasons underlying this observation are presently unknown. Disruption of endogenous host immune surveillance and promotion of tumor immune escape is one mechanism by which BRAFV600E tumors may achieve more aggressive behavior. This study evaluated the relationship between BRAFV600E status and known strategies of tumor-mediated immune suppression. Methods: Tissue sections of PTC tumors from 33 patients were evaluated by immunohistochemistry for tumor-expressed suppressive ligands and enzymes and effector and suppressor populations of tumor-infiltrating immune cells. Presence of BRAFV600E was evaluated by direct DNA sequencing of PTC specimens and the results correlated with tumor-expressed molecules and tumor-in...