A case of IgG4-related disease with rectal cancer.

A 72-year-old male with liver dysfunction and an increase in serum total protein/albumin (TP/Alb) ratio was referred to our hospital. There was a marked increase in serum immunoglobulin (Ig) G4 level (IgG/IgG4: 3,485/2,860 mg/dl). Diagnostic imaging did not reveal any enlargement of the pancreas or narrowing of the pancreatic duct. However, bilateral submaxillary gland swelling, sclerosing cholangitis, and retroperitoneal fibrosis were noted, suggesting multifocal fibrosclerosis. Histological examination of the submaxillary gland showed the infiltration of IgG4-positive plasma cells, although there was no narrowing of the pancreatic duct, leading to a diagnosis of IgG4-related disease with various extrapancreatic lesions. Systemic investigation before the introduction of steroid therapy revealed rectal cancer. After low-position anterior resection, steroid therapy was introduced, reducing the lesions. Recent studies have reported autoimmune pancreatitis/IgG4-related disease with malignant tumors. However, the association and pathogenesis remain to be clarified. Malignant tumors are detected before or after the treatment of autoimmune pancreatitis/IgG4-related disease; pretreatment diagnosis and post-treatment follow-up should be carefully performed, bearing in mind the concomitant development of malignant tumors.