Glucocorticoids are widely prescribed drugs. In the human body, glucocorticoid is the main stress hormone, and controls a variety of physiological and cellular processes, including metabolism and immune response. It belongs to the same steroid superfamily as estrogens, which are known to play a role in breast cancer. However, the effect of glucocorticoid use on the risk of breast cancer is not clear.

We conducted a case-control study using population-based medical databases from Northern Denmark (1.8 million inhabitants) to investigate the association between glucocorticoid prescriptions and breast cancer risk. The study included 9,488 incident breast cancer cases diagnosed between 1994 and 2008 and 94,876 population controls. We estimated the odds ratios (ORs) and 95% confidence intervals (CIs) associating glucocorticoid use with breast cancer occurrence, controlling for prescriptions of postmenopausal hormone replacement therapy, anti-diabetics, immunosuppressive drugs, and hospital diagnosis of obesity, diabetes, chronic pulmonary diseases and autoimmune diseases.

We found no effect on breast cancer risk in ever users (>2 prescriptions) of any glucocorticoids (adjusted OR (aOR)=1.0; 95% CI: 0.96, 1.1), systemic glucocorticoids (aOR=1.0; 95% CI: 0.96, 1.1), or inhaled glucocorticoids (aOR=1.0; 95% CI: 0.95, 1.1), each compared to never users of any glucocorticoids. Associations for recent use (preceding 2 years) and former use (more than 2 years earlier) were near null in all dose categories (low, medium and high number of prescriptions). Intensity of systemic glucocorticoid use (cumulative prednisolone equivalent doses), regardless of duration (<1, 1-5, 5+ years), was also not associated with breast cancer risk.

Overall, our study provides no evidence that glucocorticoid use affects the risk of breast cancer.

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