Lower breast cancer risk in RA unexplained by hormonal risk factors
Although the risk for breast cancer is reduced among patients with rheumatoid arthritis, there is evidence of an equally pronounced risk reduction prior to RA diagnosis that is unexplained by hormonal risk factors, according to findings published in the Annals of the Rheumatic Diseases.
“The characteristics and the reason(s) behind the decreased risk of breast cancer in women with RA remain unknown, indeed also virtually unstudied,” Hjalmar Wadström, MD, PhD, of the Karolinska Institute, in Sweden, and colleagues wrote. “Hormonal factors such as hormone replacement therapy (HRT), early menarche and late menopause, no breast feeding and nulliparity and increasing age at first birth are all established risk factors for breast cancer. The role of these factors in the occurrence of RA is less clear.”
“For HRT, available evidence does not indicate an association with risk of RA,” they added. “For breast feeding, studies to date have reported a protective effect against RA, while results for parity and risk of RA are inconclusive. Early menopause may be associated with subsequent development of RA. Importantly, however, no study has assessed the extent to which the decrease in risk of breast cancer in women with RA can be explained by known breast cancer risk factors.”
To evaluate the risk for breast cancer among patients with RA, as well as the risk for RA in those with a history of breast cancer, taking antihormonal treatment into account, Wadström and colleagues studied data from a collection of national registries in Sweden. The researchers identified 15,921 women with new-onset RA between Jan. 1, 2006, and Dec. 31, 2016, using the Swedish Rheumatology Quality Register and the National Patient Register. These patients were matched, based on age, sex and residence, to 79,441 individuals from the general population.
Through linkages with the Cancer Register, the Prescribed Drug Register, the Total Population Register, the Multigeneration Register and the Causes of Death Register, Wadström and colleagues analyzed information on breast cancer, reproductive history, hormone replacement therapy and socioeconomic factors. The researchers calculated the relative risk for breast cancer after RA using Cox regression. They also determined the relative risk for RA among those with a history of breast cancer using conditional logistic regression.
According to the researchers, the risk for breast cancer was reduced in patients with RA (HR = 0.8; 95%CI, 0.68-0.93), an association that remained even after adjusting for breast cancer risk factors. The risk for RA in those with a history of breast cancer was similarly reduced (OR = 0.87, 95%CI 0.79 to 0.95). Further, patients with breast cancer who were treated with tamoxifen (OR = 0.86; 95%CI, 0.62-1.2) or aromatase inhibitors (OR = 0.97; 95%CI, 0.69-1.37) did not demonstrate an increased risk for RA compared with those with breast cancer who were treated differently.
“We found a decreased risk of breast cancer in patients with RA, and a similar decrease in risk of RA in patients with a history of breast cancer,” Wadström and colleagues wrote. “We did not find evidence to support that the decreased risk of breast cancer was due to known risk determinants. Thus, we were ultimately unable to explain the origins of this association. Antihormonal therapy as used in secondary breast cancer pharmacoprevention does not seem to increase RA risk.” – by Jason Laday
Disclosures: Wadström reports no relevant financial disclosures. Co-author Johan Askling, MD, PhD, of the Karolinska Institute and Karolinska University Hospital, reports research agreements with AbbVie, Astra-Zeneca, BMS, Eli Lilly, MSD, Pfizer, Roche, Samsung Bioepis and UCB. The Karolinska Institute has received remuneration for Askling participating in advisory boards arranged by Pfizer and Lilly.