Does RA Increase the Risk of Breast Cancer in Women?

Women with rheumatoid arthritis (RA) develop breast cancer at lower rates than the general population, and women with breast cancer who receive hormonal therapy do not have an increased risk of developing RA, according to new research.

For their study, the researchers used national Swedish registers to identify women who were newly diagnosed with RA from 2006 to 2016 and matched them according to age, sex, and residence to 5 women randomly selected from the general population.

The study team gathered data on breast cancer diagnoses, breast cancer risk factors—including reproductive history and use of hormone replacement therapy—and socioeconomic status. Cox regression analysis was used to assess the relative risk of women with RA developing breast cancer, and conditional logistic regression was used to assess the relative risk of women who had had breast cancer and later developed RA.

The results revealed that women with RA had a reduced risk of incident breast cancer, which was not weakened by adjusting for other risk factors for breast cancer in these study participants. Similarly, women who had a history of breast cancer showed a reduction in risk of developing RA.

Participants whose breast cancer had been treated with tamoxifen or aromatase inhibitors showed no increase in risk of RA when compared with women who had received different kinds of treatment for breast cancer.

“In conclusion, 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,” the researchers 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.”

—Rebecca Mashaw

Reference:

Wadström H, Pettersson A, Smedby KE, Askling J. Risk of breast cancer before and after rheumatoid arthritis, and the impact of hormonal factors. Annals Rheum Dis. 2020;79(5):581-586. http://dx.doi.org/10.1136/annrheumdis-2019-216756