Breast cancer remains the most commonly diagnosed cancer among women worldwide. According to the World Health Organization (WHO), more than 99% of breast cancer cases occur in women, with fewer than 1% diagnosed in men. Each year, an estimated 2.3 million women are affected globally. Around three-quarters of these cases are classified as estrogen receptor–positive (ER-positive), meaning tumor growth is driven by the hormone estrogen.
The standard treatment for ER-positive breast cancer involves anti-estrogen therapies, such as letrozole, which suppress the body’s estrogen production to reduce the risk of cancer recurrence. While effective, these medications often come with significant side effects that resemble menopausal symptoms, including hot flashes, joint and muscle pain, bone density loss, and elevated cholesterol levels. These adverse effects can make long-term treatment difficult for many patients.
New findings from the PIONEER study, led by researchers at the University of Cambridge and published in Nature Cancer, suggest a promising way to address both treatment tolerance and tumor control. The study found that artificial progesterones, specifically megestrol acetate—commonly prescribed to ease menopause-like symptoms—may also help slow the growth of ER-positive breast tumors.
Researchers discovered that even low doses of megestrol acetate, when used in combination with letrozole, significantly reduced tumor cell proliferation. This indicates that the drug may offer dual benefits: alleviating the side effects of anti-estrogen therapy while enhancing its effectiveness against cancer.
The clinical trial included 244 women with early-stage breast cancer treated across 10 hospitals in the United Kingdom. Participants were divided into three different treatment groups to assess the impact of combining megestrol acetate with standard therapy.
While the results are encouraging, researchers caution that further studies are needed to confirm the long-term benefits and safety of this approach. If validated, the combination therapy could improve patient adherence to treatment and provide better overall tumor control for one of the most common forms of breast cancer.
