BTK and head and neck cancer: In head and neck cancer, adenosine (ADO)‐producing Bregs have been identified.[64] These extracellular ADOs bind to their corresponding receptors on effector B cells and inhibit intracellular Bruton's tyrosine kinase (BTK) and Ca2+ influx, which leads to aberrant BCR signaling and limiting B cell activation and antibody production.[64] In addition, in pancreatic cancer, IL‐35 produced by Bregs upregulates BCL6, a transcriptional regulator in naive B cells, through stimulation of the STAT3‐PAX5 complex.