Comparison of histopathological features of pancreatic carcinoma and type 1 autoimmune pancreatitis

Type 1 autoimmune pancreatitis ( AIP ‐1) is an immunoglobulin G ( IgG )‐4‐related disease ( IgG 4‐ RD ), characterized by elevated serum immunoglobulin G 4 ( IgG 4) and infiltration by IgG 4 + plasma cells. Pancreatic carcinoma ( PC ) sometimes shows infiltration by IgG 4 + plasma cells, but details have been unclear. We compared pathological findings and expression of IgG 4 and IgG in fibroses in 18 PC patients to those from 9 AIP ‐1 patients. Fibroses were divided into areas of ductal adenocarcinoma ( DA ) and obstructive pancreatitis ( OP ). Serum IgG 4 levels were lower than the cut‐off value in all PC patients with no IgG 4‐ RD . Diffuse lymphoplasmacytic infiltration and eosinophil infiltration were characteristic of fibroses in PC . Though AIP ‐1 samples often had storiform fibrosis even in biopsies, PC did not show storiform fibrosis. Ratios of IgG 4 + plasma cells/ IgG + plasma cells ( IgG 4/ IgG ratios) in DA and OP were significantly lower than in AIP ‐1. However, high‐density IgG 4 + plasma cell foci were detected in PC fibroses, particularly around peripheral nerves, vessels, and lymphoid follicles; between lobules and invasion fronts; and within neutrophilic abscesses. In conclusion, the IgG 4/ IgG ratio is useful in distinguishing PC from AIP ‐1, and should be evaluated in three or more areas, as PC can show localized high‐density IgG 4 + plasma cell areas.