TNF inhibitors pose no important risk of lymphoma in patients with rheumatoid arthritis, the latest data from a large British registry confirms.

Dr Louise Mercer and colleagues at the University of Manchester compared 11,931 patients with RA who had commenced a TNF inhibitor since 2001 and 3,367 who were treated with conventional DMARDs.

The incidence of lymphoma per 100,000 patient years was 88 in the TNF cohort and 154 in the biological naive cohort. After adjusting for a number of confounders, they calculated the hazard ration was exactly 1.00.

“No risk differences were observed for any individual TNF inhibitor,” they said.

The analysis was based on the prospective British Society for Rheumatology Rheumatoid Arthritis Register, which includes more than 120,000 patient years of data on patients taking biological or non-conventional DMARDs.

It was prompted by continuing concern about lymphoma risks associated with RA itself, and also with its treatment.

“Patients with rheumatoid arthritis are at increased risk of lymphoma compared with the general population. There are concerns that TNF inhibitors may exacerbate this risk,” they said.

“However, since the excess risk of lymphoma in RA is related to the cumulative burden of inflammation, TNF inhibitors may conversely reduce the risk of lymphoma by decreasing the burden of inflammation.”

A landmark Swedish study published in 2006 found that patients in the highest decile of cumulative RA disease activity had a more than 60-fold increase in lymphoma risk compared to those in the lowest decile.

The British study is one of the largest and most detailed analyses of TNF inhibitors and lymphoma risk published to date and mirrors the results of other cohort studies and meta-analyses, the researchers said.

Its strengths include the inclusion only of patients commencing TNF inhibitors as their first biologic drug, close linkage with comprehensive UK cancer registries, careful confirmation of all lymphoma diagnoses, and exclusion of possible pre-existing cases diagnosed within the first 6 months of biologic treatment.

The most common type of lymphoma was diffuse large B cell lymphoma, followed by follicular lymphoma.

“Further follow-up of significantly larger populations is now needed to determine whether longer-term exposure or cumulative drug exposure influences risk, given the overall low absolute risk of lymphoma in TNF inhibitor-treated patients,” they concluded.