Risk of cancer for patients with rheumatoid arthritis versus general population: a national claims database cohort study.

Background: Older studies uncovered an increased risk of cancer in patients with rheumatoid arthritis between 10% and 30% compared to the general population, with a lack of data concerning infrequent cancers. In recent year, major therapeutic breakthroughs might have affected this risk of cancer by mitigating disease activity or on the contrary by impairing antitumoral immune response. The objectives of this study are to compare cancer risk in patients with treated rheumatoid arthritis to the general population, in all treated patients and according to treatment exposure.

Methods: This is a nationwide population-based study within the French national claims database "Système National des Données de Santé" (SNDS) between January 1st 2010 and December 31st 2020, to estimate the age and sex-standardized incidence ratios of cancer (all sites and site specific) of treated rheumatoid arthritis patients, with the French population as reference (by use of the French Network of Population-Based Cancer Registries [FRANCIM]).

Findings: During the study period, 257,074 treated patients with rheumatoid arthritis contributed to a total of 2,098,238 person-years for the main analysis. The all-cancer risk was increased in rheumatoid arthritis patients, with a SIR (Standardized Incidence Ratio) of 1.20 (95% CI [1.17-1.23]). This risk was increased particularly for lung (SIR 1.41, 95% CI [1.36-1.46], bladder (SIR 2.38 95% CI [2.25-2.51]), cervix (SIR 1.80, 95% CI [1.62-2.01]), prostate (SIR 1.08, 95% CI [1.04, 1.13]) cancers, melanoma (SIR 1.37, 95% CI [1.29-1.46]), diffuse large B cell lymphoma (SIR 1.79, 95% CI [1.63-1.96], multiple myeloma (SIR 1.42, 95% CI [1.27-1.60]) and Hodgkin's lymphoma (SIR 2.73, 95% CI [2.31-3.23]). Some cancers were less frequent than in the general population such as pancreatic (SIR 0.90, 95% CI [0.83-0.97]) as well as breast and endometrial cancers (SIR 0.91, 95% CI [0.88-0.94] and SIR 0.77, 95% CI [0.71-0.84] respectively). Although we observed a modest but significant relative increase of all-cancer risk over-time in rheumatoid arthritis patients, there was a trend towards a decrease in risk of non-Hodgkin's lymphoma. Patients treated with rituximab were the patients displaying the highest risk of cancer.

Interpretation: Compared to the general population, treated rheumatoid arthritis patients were at greater risk of all-cancer and some site specific cancers, except for breast, pancreatic and endometrial cancers which were less frequent than in the general population.

Funding: This work was supported by unrestricted grants from the InCA (national institute against cancer) and AP-HP (Assistance Publique des Hôpitaux de Paris).