The Effect of Antiestrogen Agents on Risk of Autoimmune Disorders in Patients with Breast Cancer

Objective. To investigate the relationship between antiestrogen therapy in women with breast cancer and risk of autoimmune disease. Methods. We used a national database to assess the incidence of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) following treatment with selective estrogen receptor modulators (SERM) or aromatase inhibitors (AI) in women with breast cancer. The total number of patients in our study was 190,620. Results. We observed highly significant, cumulative dose-dependent increased OR of incidence of both SLE and RA following treatment with SERM (p < 0.0001). The odds of developing RA were also increased following AI therapy (p < 0.001), but there was a trend for reduced odds of SLE, though this trend did not attain statistical significance (p = 0.070 for 2-11 months of treatment and p = 0.254 for 12+ months of treatment). Conclusion. Antiestrogen agents may have an important effect on risk of autoimmune disease.