[Immunoglobulin G4 disease with pancreatic affectation: the mimicker of malignancy].

Background: mmunoglobulin G subclass 4-related disease (IgG4-RD) is characterized by elevated serum IgG4 levels and tissue infiltration by IgG4-positive plasma cells. It has a varied clinical presentation, and definitive diagnosis requires rigorous clinicopathological correlation.

Clinical case: 47-year-old male patient with a history of weight loss of 35 kg over 2 years, accompanied by the presence of pulmonary nodules and alterations in pancreatic morphology detected by imaging, which was assessed as a probable pancreatic neoplasm; however, IgG4-RD was suspected during the approach, which is why serum IgG4 levels and a biopsy of the submandibular gland were requested, fulfilling the diagnostic criteria, consequently starting treatment with rituximab with an adequate response.

Conclusion: IgG4-RD is a rare disease that many times is not considered as a differential diagnosis, leading to diagnostic delays.