Potential risk factors for mucous involvement include earlier age at onset, drugs such as dipeptidyl peptidase-4 inhibitors, cancer, and blood/serum biomarkers, including lower eosinophil count, higher erythrocyte sedimentation rate, IgG autoantibodies against both the NH2- and COOH-termini of BP180, and the absence of anti-BP230 antibodies. Here, DPP4 is linked to cancer.