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.