SAN FRANCISCO – Rheumatoid arthritis conferred a doubling of the risk of lymphoma when compared against the general population in a large Swedish registry study, regardless of the patients’ experience with biological disease-modifying antirheumatic drugs.
But patients who took biological disease-modifying antirheumatic drugs (bDMARDs) had a sixfold greater risk of natural killer or T-cell lymphoma than did the general population, and that association was about four times stronger than for patients who had never taken biologics, reported Dr. Karin Hellgren, who led the study at the Karolinska Institute in Stockholm. That finding in particular shows the need to keep studying the links between bDMARDs and specific lymphoma subtypes, he said.
Severe rheumatoid arthritis seems to strongly increase the risk of lymphoma (Arthritis Rheum. 2006;54:692-701), but researchers have debated whether the reason relates to bDMARDs or RA itself. Clinical trials have produced conflicting results; observational studies have reported no overall link between bDMARDs and lymphoma, but have raised questions about long-term exposure, the effects of individual agents, and lymphoma subtypes, Dr. Hellgren said at the annual meeting of the American College of Rheumatology.
To delve deeper into these issues, he and his associates compared 15 years of data for 13,240 RA patients on bDMARDs from the Swedish Biologics (ARTIS), Patient, and Cancer Registers and a national cohort of 46,568 bDMARD-naive patients. The researchers also compared both groups with 458,846 age- and gender-matched adults from the Swedish Population Register, following individuals until the end of 2012 or until lymphoma diagnosis, death, emigration, or bDMARD initiation, in the case of the naive patients.
Overall, patients with RA averaged one diagnosis of lymphoma per 1,000 population, compared with 0.5 cases per 1,000 for the overall population of Sweden, Dr. Hellgren said. In terms of absolute numbers, there were 241 cases of lymphoma among bDMARD-naive patients, 1,413 cases in the general population, and 69 cases among patients on bDMARDs, including 68 who were taking TNF inhibitors. The average age of the latter group of patients was 57 years. They had been diagnosed with RA at about age 50, had a mean 28-joint Disease Activity Score score of 5.3, and averaged 5.9 years of exposure to TNF inhibitors. Their risk of any type of malignant lymphoma was about 20% higher than for bDMARD-naive patients, but the difference was insignificant overall and in subgroups stratified by gender, age, and year starting treatment. Likewise, although patients were at greater risk of lymphoma if they had been on bDMARDs for 5-15 years (hazard ratio, 1.9) than for less time (HRs, about 1.0), there was no significant difference in risk compared with bDMARD-naive patients.
“There also were no statistically significant differences between drugs,” including infliximab (Remicade), etanercept (Enbrel), and adalimumab (Humira), Dr. Hellgren said. “In terms of the newer TNF inhibitors and other biologics, data are still too scarce to evaluate,” he added. Both exposed and bDMARD-naive patients were at especially high risk of Hodgkin lymphoma and diffuse large B-cell lymphoma, compared with the general population, but the strongest association of all was between bDMARD exposure and natural killer or T-cell lymphoma (HR, 6.0; 95% CI, 2.7-13.3). “The distribution of lymphoma subtypes warrants further assessment,” Dr. Hellgren concluded.
The ARTIS registry is funded by AbbVie, Bristol-Myers Squibb, Roche, Merck, Pfizer, Sobi, Lilly, and UCB. Dr. Hellgren had no disclosures. One coauthor reported financial relationships with AstraZeneca, Pfizer, UCB, Roche, Merck, Bristol-Myers Squibb, and AbbVie.