A study in the Netherlands has discovered that corticosteroids, widely used anti-inflammatory drugs, may prolong the effect of hormone therapy for breast cancer in mice. 

Most breast cancers are responsive to the hormones progesterone and oestrogen, and women receive hormone therapy to block cancer growth and suppress the disease. However, cancer can become resistant to therapy, requiring more intensive treatments such as chemotherapy. 

Researchers from the EARA member Netherlands Cancer Institute (NKI) were intrigued by a discovery from the University of Genoa, Italy, showing that patients on a low-calorie diet may respond better to hormone therapy.  

In collaboration with the study leaders and Oncode Institute, Netherlands, they found that, in mice with breast cancer responsive to hormones and patients’ blood, a restrictive diet led to a rise in cortisol, a natural corticosteroid produced in response to stress.  

In mice, the researchers found that fasting activates genes responsive to cortisol in cancer cells, increasing the efficacy of hormone therapy. The effects of fasting could be mimicked by dexamethasone, another clinically used corticosteroid. 

“These findings suggest that we may have uncovered a new application for this widely used and inexpensive medication, which may be able to replace or delay more intensive, expensive treatments,” said Wilbert Zwart, co-leader of the study published in Nature and researcher at NKI.

A phase II clinical trial at NKI Hospital will begin in 2026, enrolling 80 patients with breast cancer who no longer respond to hormone therapy. Along with this therapy, patients will be treated with dexamethasone.