The goal of this observational, retrospective study is to learn about cancer risk in autoimmune pancreatitis (AIP) patients. The main questions it aims to answer are:

• Do patients with AIP have higher incidence of cancer in comparison to general population?
• What is the overall prevalence of cancer in AIP patients?
• What are the characteristics of AIP patients associated with the incidence of cancer?

Autoimmune pancreatitis (AIP) is a relapsing form of pancreatitis, comprising two histological entities with differing clinical, serological, and prognostic characteristics. Type 1 AIP is a pancreatic manifestation of IgG4-related disease, while type 2 AIP is an isolated pancreatic disorder strongly associated with the simultaneous occurrence of inflammatory bowel disease (IBD). AIP patients, particularly type 1, face a risk of relapse and may develop exocrine and endocrine pancreatic insufficiency. While it's widely acknowledged that chronic pancreatitis increases the risk of pancreatic cancer, the association between AIP and pancreatic cancer remains more controversial. AIP can imitate pancreatic cancer, and coincidence has been reported. Retrospective data from Japan suggested a high risk of pancreatic cancer and bile duct cancer in patients with AIP. However, there is a paucity of specific data on the relationship between AIP and pancreatic cancer. Japanese studies have suggested a higher incidence of extrapancreatic cancer in AIP patients compared to the general population. German single-center data support this claim. The most frequently reported cancers include lung, gastric, and prostate cancer, constituting approximately 50% of all cancers detected at or after the diagnosis of AIP. However, the time span of both AIP and cancer was not defined and might have introduced bias. Available data need to be interpreted with caution as no studies have yet compared the incidence of the most common cancers in AIP patients directly to age-grouped and gender-matched controls in the general population.

To address this lack of knowledge a worldwide, multicenter, retrospective cohort study of AIP patients is initiated founded in the Pancreas2000 framework. With this trial cancer incidence and prevalence will be assessed for AIP patients and compared to age-matched controls.

The trial is based on a REDCap questionnaire containing following information.

1. Demographic details Month and year of birth Survival status month and year of death, if applicable Gender (Male, Female) Ethnicity (Caucasian, Hispanic, African, Asian, Arabic, Other, Unknown) Weight and height for the purpose of calculating body mass index Tobacco status (Current, Former, Never) incl. "smoking pack-years" if applicable Alcohol consumption (Current daily, current occasionally, Former, Never, Not available) History of other autoimmune diseases (not IgG4-related) (No, Sjögren's' syndrome, Rheumatoid arthritis, Sarcoidosis, Autoimmune thyroiditis (NOT IgG4 related), Other) History of inflammatory bowel disease (Yes, No, Unknown) Family history of cancer (Yes, No, Unknown)
2. AIP characteristics Month and year of diagnosis AIP The classification system used for original diagnosis (ICDC, HISORT, Asian, Unify) ICDC diagnosis type (Type 1, Type 2, Not otherwise specified (NOS) AIP) ICDC diagnosis level (Definite, Probable) ICDC parameters fulfilled for diagnosis (Histology, Serum IgG4, Imaging, Improvement after steroid treatment, Other organ involvement) Serum IgG4 (1-2 over upper limit, >2 over the upper limit, >4 over the upper limit) Imaging (Focal enlargement, Whole organ enlargement (sausage-like), Other) Other organ involvement (Salivary/lacrymal glands, Retroperitoneum/ kidneys, Bile ducts/liver, Musculoskeletal system, Gastrointestinal tract: Intestines, colon, esophagus, Vasculitis (e.g., aortitis), Enlarged lymph nodes, IBD) Presenting symptoms of AIP (None, Jaundice, Acute pancreatitis, Weight loss, Abdominal pain, New onset of diabetes) Medical treatment for AIP (Prednisone, Rituximab, Azathioprine, 6-mercaptopurine, Methotrexate, Mycophenolate mofetil, other) Interventional treatment for AIP (Partial pancreatectomy, Biliary stent placement, Other) AIP relapse (No relapse, 1-2 relapse(s), 3-4 relapses, >5 relapses, Unknown) AIP-related complications (No, Diabetes mellitus, Pancreatic exocrine insufficiency, Other) Month and year of last contact
3. Cancer Diagnosis Month and year of diagnosis of cancer Number of cancer diseases (1,2,3,4) Cancer type (list according to the World Health Organization) Cancer-related death (yes, no) In case of more than one cancer, specifically which cancer caused death

Inclusion Criteria:

• Patients diagnosed with AIP after 2005, including type 1, type 2, and not-otherwise-specified (NOS) AIP, regardless of the diagnostic criteria used.

Exclusion Criteria:

• Patients younger than 18 years at last contact
• Patients with less than 12 months of follow up after diagnosis
• Patients with immune checkpoint inhibitor-induced pancreatitis

Tertiary centers specializing in the treatment of pancreatitis worldwide will be invited to participate in the study. Patients with AIP will be identified locally, and information for characterization of risk factors, AIP, and cancer will be retrospectively extracted from the medical files. The core group comprises six centers from Denmark, Germany, Slovenia, and Estonia.

IPD will be available only to core group, not other researches. Core group retains right to perform post-hoc analyses, these proposals will be reviewed and granted by the steering committee.