Risk of Cancer in Patients with Rheumatoid Arthritis Compared with the General Population: A Nationwide Cohort Study in Lithuania

<i>Background and Objectives</i>: Rheumatoid arthritis (RA) is a multisystem autoimmune disease that needs immunosuppressive treatment. Previously, studies have shown an increased risk of cancer in patients with RA compared with the general population. The purpose of this study was to explore the associations between RA and cancer risk, providing updated insights into the incidence of specific cancers in patients with RA. <i>Materials and Methods</i>: A total of 746 cancer cases were observed, with the most common types being nonmelanoma skin cancer (139 cases), breast cancer (87 cases), lung cancer (47 cases), and Hodgkin lymphoma (43 cases). <i>Results:</i> Compared with the general Lithuanian population, patients with RA had an increased overall cancer risk, with an SIR of 1.17 and 95% CI of 1.09-1.26. Hematological cancers and nonmelanoma skin cancers were the most common types of cancer in the RA population, and patients with RA had a significantly greater risk of site-specific cancers (non-Hodgkin lymphoma: SIR 4.19, 95% CI 1.57-11.18; Hodgkin lymphoma: SIR 3.03, 95% CI 2.11-4.36; myeloma: SIR 3.00, 95% CI 1.84-4.90; leukemia: SIR 2.39, 95% CI 1.62-3.54; and skin nonmelanoma: SIR 1.54, 95% CI 1.27-1.83). Male patients with RA had an increased risk of prostate and kidney cancer (SIR 1.40, 95% CI 1.12-1.75; SIR 1.85, 95% CI 1.11-3.06). Our study revealed a significantly lower risk of colorectal cancer among patients with RA. Additionally, we observed a statistically significant reduction in the risk of mouth and pharynx cancers; however, this finding was based on only three observed cases. <i>Conclusions:</i> Patients with RA remain particularly affected by an increased cancer risk. Knowing these risks, we need clear recommendations for specific screenings in patients with RA, which could allow for early diagnosis and better cancer treatment in the early stages.