Women with rheumatoid arthritis (RA) have a lower risk of breast cancer compared with the general population, but researchers believe factors independent of RA may explain this association, according to a study in the Annals of Rheumatic Diseases.
The study included 15,921 women from nationwide Swedish registers who were diagnosed with incident RA between 2006 and 2016. Another 79,441 randomly selected individuals from the general population were matched to the RA group on age, sex, and residence.
Information was collected on each individual’s breast cancer incidence, breast cancer risk factors, and socio-economic background. The researchers used Cox regression analyses to evaluate the relative risk of breast cancer after RA diagnosis, while conditional logistic regression analyses were used to assess the relative risks of RA in women with a breast cancer history.
At time of study entry, the mean ages were 59 years in both the RA and matched control groups. A total of 10 patients in the RA group and 4 patients in the general population group had a first-degree relative with RA, while 10 patients in each group had a first-degree relative with breast or ovarian cancer.
In the women with RA, the risk of incident breast cancer was reduced compared with the general population (hazard ratio, 0.80; 95% CI, 0.68-0.93). The investigators found that the apparent protective association between RA and reduced breast cancer risk was no attenuated after adjustment for breast cancer risk factors.
Additionally, women with breast cancer had a similar reduced risk in RA (odds ratio [OR], 0.87; 95% CI, 0.79-0.95), possibly due to the use of tamoxifen and aromatase inhibitors. There was no increased risk of RA in women with breast cancer who were treated with tamoxifen (OR, 0.86; 95% CI, 0.62-1.20) or aromatase inhibitors (OR, 0.97; 95% CI, 0.69-1.37) compared with women with breast cancer who were not treated with these therapies.
Limitations of this study included the reliance on data from nationwide registers as well as the lack of data on certain risk factors for RA and breast cancer, such as early menarche and menopause.
While the investigators noted they “were ultimately unable to explain the origins of this association” between RA and reduced breast cancer risk, they concluded that “antihormonal therapy as used in secondary breast cancer pharmacoprevention does not seem to increase RA risk.”
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
Wadström H, Pettersson A, Smedby KE, Askling J. Risk of breast cancer before and after rheumatoid arthritis, and the impact of hormonal factors. Ann Rheum Dis. 2020;79(5):581-586. doi:10.1136/annrheumdis-2019-216756