Abstract 29: Autoimmune diseases and the risk of cancer
Authors: Heikkinen Sanna , Tanskanen Tomas , Sipilä Lauri , Pitkäniemi Janne 
Published: June 2022

Background: Many autoimmune diseases (AD) are known to be associated with comorbidities, and certain ADs have been suggested to influence cancer risk. Immunosuppression and dysregulation of the immune system promote the development of certain cancers, particularly hematological malignancies. There is also evidence on an increased risk of several types of solid tumors among individuals with an AD. The aim of this population-based cohort study was to evaluate the risk of any cancer, except non-melanoma skin cancer, in 31 different ADs. We explored associations between both common (such as rheumatoid arthritis) and rare (such as Behcet’s disease) ADs and cancer.

Material and methods: The data consists of a population-based random sample of 2.5 million individuals who lived in Finland on January 1, 2000. It includes information on hospital diagnoses between 1970 and 2017 for each individual, with a total of 92 million hospital care records. There were 70 694 individuals with prevalent AD and 68 002 individuals with prevalent cancer. Those with prevalent cancer were removed from the analyses. Participants were followed up for subsequent occurrence of cancer, based on data from the nationwide cancer registry. We estimated relative risks (RRs) with 95% confidence intervals (CIs) using piecewise constant hazard regression models, adjusting for age, sex, and calendar period. Time since AD diagnosis was treated as a time-varying covariate.

Results: During the follow-up, 222 211 primary cancers were diagnosed, 18 409 with and 203 802 without a pre-existing AD. Overall, the risk of cancer was 2.02 (95% CI 1.93-2.12) for &lt;1 year since any AD diagnosis and 1.05 (1.03-1.07) for ≥10 years since diagnosis. The largest increase in cancer risk was observed for individuals with autoimmune hemolytic anemia, and there was evidence of a persisting risk even after 10 years since diagnosis (RR 8.53 (6.76-10.77) for &lt;1 year since diagnosis and 1.62 (1.18-2.24) for ≥10 years since diagnosis). Long-term impact on cancer risk was also observed for autoimmune vasculitis, Crohn's disease, discoid lupus erythematosus, pemphigus, psoriasis, systemic lupus erythematosus and ulcerative colitis. For individuals with these ADs, cancer risk was still elevated after 10 or more years after AD diagnosis.

Discussion: Cancer incidence was greatly dependent on AD duration. Cancer risk was increased soon (&lt;1 year) after AD diagnosis in 24 different ADs and elevated risks were still observed after ≥10 years in 8 ADs.

Cancer and comorbid diseases may have partly shared etiologies. Many lifestyle factors such as smoking, alcohol consumption, and obesity are established causes of many common diseases. Also, AD treatments may in some cases be tumorigenic. In conclusion, many ADs were associated with a significantly increased risk of cancer long after diagnosis, and this should be considered in patient counseling and monitoring. The findings also encourage search for shared risk factors underlying both diseases.

Citation Format: Sanna Heikkinen, Tomas Tanskanen, Lauri Sipilä, Janne Pitkäniemi. Autoimmune diseases and the risk of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 29.