IgG4-Related Diseases-Continues To Be a Cancer Mimicker.

Immunoglobulin G4-related disease (IgG4-RD) is a chronic multisystem immune-mediated disease. Histologically, it presents as infiltration with IgG4-secreting plasma cells affecting many organs such as the pancreas, lacrimal glands, salivary glands, kidneys, and arteries, resulting in chronic fibrosis and scarring within the tissue which over time forms into a mass. It is a slow-growing process that usually remains indolent until it causes a mass effect or tissue infiltration. Our patient was found to have a pancreatic mass on imaging concerning pancreatic neoplastic lesions. He subsequently underwent biopsy for histology/pathology and IgG4 levels, which led to our diagnosis of IgG4-RD. Imaging, blood tests, and, most importantly, histopathological features of the involved organ are important in determining the diagnosis. This is important as a treatment plan will be based on the given diagnosis, and patients with IgG4-RD respond very well to systemic steroid therapy.