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 (IgG4-RD), characterized by elevated serum immunoglobulin G4 (IgG4) and infiltration by IgG4(+) plasma cells. Pancreatic carcinoma (PC) sometimes shows infiltration by IgG4(+) plasma cells, but details have been unclear. We compared pathological findings and expression of IgG4 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 IgG4 levels were lower than the cut-off value in all PC patients with no IgG4-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 IgG4(+) plasma cells/IgG(+) plasma cells (IgG4/IgG ratios) in DA and OP were significantly lower than in AIP-1. However, high-density IgG4(+) 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 IgG4/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 IgG4(+) plasma cell areas.