Ascertainment of autoimmune conditions and other exposures

Forty-five autoimmune conditions identified by International Classification of Diseases 9^th edition (ICD-9) codes from Medicare claims were included in this study (online supplementary table 1). A diagnosis of autoimmune condition was defined as having a minimum of one inpatient claim (MeDPAR) or two physician/outpatient (NCH or Outpatient) claims at least 30 days apart. We required autoimmune conditions be diagnosed at least 12 months before cancer diagnosis/control selection to minimize surveillance bias and reverse causation.

We used ICD-9 codes from Medicare claims for certain medical conditions as surrogate measures for smoking and heavy alcohol use. Subjects with chronic obstructive pulmonary disorder (COPD; except asthma, 490, 491, 492, 494, 495, or 496), personal history of tobacco use (V15.82) or non-dependent tobacco use disorder (305.1) were considered smokers and those with any alcohol-induced liver disorders (571.0, 571.1, 571.2, 571.3), alcohol-induced psychiatric or neurologic disorders (291), alcohol intoxication (303), non-dependent alcohol abuse (305), or a personal history of alcoholism (V11.3) were classified as heavy alcohol users. Type 2 diabetes (250.00, 250.02, 250.10, 250.12, 250.20, 250.22, 250.30, 250.32, 250.40, 250.42, 250.50, 250.52, 250.60, 250.62, 250.70, 250.72, 250.80, 250.82, 250.90, 250.92, 790.2), overweight/obesity (278.0, 278.01, 278.02, 278.1, V77.8, 783.1, 278.00, 278.01), and chronic/acute pancreatitis (577.0, 577.1) diagnoses were also determined with ICD-9 codes.