Pancreatic Cancer Mimicking Relapse of Autoimmune Pancreatitis: Case Reports

INTRODUCTION: Although pancreatic cancer rarely co-occurs with autoimmune pancreatitis (AIP), distinguishing between AIP relapse and pancreatic cancer remains difficult, potentially leading to delayed diagnosis. A recent nationwide survey in Japan indicated that pancreatic cancer underlies a significant proportion of cancer-related deaths among patients with AIP. CASE PRESENTATION: Here, we present two cases of pancreatic cancer that initially mimicked AIP relapse. Case 1: An 89-year-old man with a long-standing history of pancreatic enlargement began steroid therapy for suspected AIP based on elevated serum IgG4 levels. Although IgG4 levels initially decreased following the treatment, they subsequently rose again, accompanied by worsening pancreatic swelling. Endoscopic ultrasound-fine-needle aspiration (EUS-FNA) revealed adenocarcinoma. Case 2: A 76-year-old woman with AIP, diagnosed based on focal pancreatic body enlargement and elevated IgG4, experienced multiple steroid-responsive relapses over 8 years. Whiletapering steroids, a new pancreatic nodule was detected on MRI, which was characterized by high signal intensity on diffusion-weighted imaging. Although the initial EUS-FNA was negative for carcinoma, a repeat biopsy 10 months later confirmed pancreatic cancer. Both patients underwent laparoscopic or robotic distal pancreatectomy with lymphadenectomy, and histopathological analysis confirmed pancreatic cancer arising in severely AIP-affected pancreatic tissue. CONCLUSIONS: In patients showing clinical or radiological worsening during AIP follow-up, repetitive diagnostic evaluations are warranted to facilitate the timely detection of underlying pancreatic cancer.