Abstract
OBJECTIVE: To determine to what extent the observed experience of breast cancer in a combined cohort of patients with systemic lupus erythematosus (SLE) could be explained by the profile of breast cancer risk factors. METHODS: Data were pooled from 2 centers, the Montreal General Hospital and the Feinberg School of Medicine at Northwestern University in Chicago. For each female cohort member, the probability of developing breast cancer during followup was estimated based on factors (including the individual's age, parity, age at first live birth, age of menarche, personal history of benign breast disease, and family history) using the Gail model, an established model for predicting breast cancer risk. The actual occurrence of cancer cases was determined by linkage with regional cancer registries. RESULTS: Of the 583 women in the combined cohort, 5 had been diagnosed with breast cancer prior to cohort entry, and 14 declined participation. In those remaining, 12 cases of breast cancer occurred compared to 5.6 predicted by the Gail model (standardized incidence ratio 2.1, 95% confidence interval: 1.1, 3.7). Thus, after controlling for risk factors, the incidence of breast cancer was elevated. CONCLUSION: Our data suggest that the risk of breast cancer in our SLE cohort is not completely explained by traditional factors found in the Gail model. Other factors, such as carcinogenic exposures (i.e., alkylating agents and immunosuppressive drugs) or the immunologic dysregulation of SLE itself, may be contributory.
