Risks and characteristics of pancreatic cancer and pancreatic relapse in autoimmune pancreatitis patients

Background and Aim We examined the differences in the risks and characteristics of pancreatic relapse (PR) and pancreatic cancer (PC) in patients with autoimmune pancreatitis (AIP). Methods We retrospectively reviewed 123 type 1 AIP patients with a median follow‐up of 55 months (interquartile range, 27–98). The following items were evaluated: (i) cumulative relapse rates and risk factors, (ii) the incidence of PC, (iii) PR versus PC, and (iv) outcomes after the appearance of morphological changes in the pancreas (focal enlargement, apparent mass lesions, or main pancreatic duct dilation). Results (i) The cumulative PR rates were 1.7% within 1 year, 11.5% within 3 years, and 22.6% within 5 years. Lack of maintenance therapy, IgG4‐related sclerosing cholangitis, and IgG4‐related kidney disease were identified as independent predictors of relapse. (ii) Two patients (1.6%) were diagnosed with PC at 17 and 22 months after initial AIP diagnosis. (iii) Thirteen (59.1%) and four (18.2%) patients with PR had focal enlargement and main pancreatic duct dilation, respectively. The median CA19‐9 level at initial diagnosis was significantly higher in PC patients (21 vs 220.5 U/mL, P = 0.014). (iv) Eight PR patients underwent endoscopic ultrasound‐guided fine‐needle aspiration, none of whom had malignant findings. PC was diagnosed by ultrasound‐guided fine‐needle aspiration in both cancer patients. Conclusions Although the incidence of PC is low, it may mimic PR in AIP patients. Surveillance is important, and when morphological changes occur, biopsy and evaluation of serum IgG4 and CA19‐9 levels (particularly if the levels were high before) should be considered.