Archive · 10 Jan 2026
Low-Dose Megestrol Slows ER-Positive Breast Cancer Growth
Doctors often use a medicine called letrozole to treat a type of breast cancer called ER-positive breast cancer.
However, letrozole can cause hot flashes and other side effects.
Another medicine, megestrol acetate, is sometimes given to help with these hot flashes.
Researchers found that megestrol acetate, even at low doses, can also slow down the growth of breast cancer tumors.
This is good news because it means patients might get the benefits of megestrol without needing high doses, which can have more side effects.
The study involved 244 women and showed that both low and high doses of megestrol worked equally well in slowing tumor growth.
This could help patients stick to their treatment for longer, which is important because these treatments often last for many years.
Megestrol acetate, used to treat hot flashes from letrozole therapy, was found to slow the growth of ER-positive breast cancer tumors.
The PIONEER trial involved 244 women with early-stage ER-positive breast cancer across 10 hospitals in the UK.
Participants were divided into three groups: letrozole alone, letrozole with 40 mg megestrol, and letrozole with 160 mg megestrol.
Both doses of megestrol showed similar effectiveness in slowing tumor growth, with no significant difference between the two doses.
Megestrol acetate has potential side effects including weight gain, increased blood pressure, and blood clots.
- Who
- Researchers from Cambridge, United Kingdom, and 244 women with early-stage ER-positive breast cancer
- What
- A study found that low-dose megestrol acetate, used to treat hot flashes from letrozole therapy, also slows the growth of ER-positive breast cancer tumors
- When
- The study was published in Nature Cancer, with the trial conducted prior to the publication
- Where
- The trial was conducted across 10 hospitals in the United Kingdom
- Why
- To evaluate the effects of megestrol acetate on tumor growth and to mitigate side effects of letrozole therapy
- Study Name
- PIONEER trial
- Lead Researchers
- Cambridge, United Kingdom
- Participants
- 244 women with early-stage ER-positive breast cancer
- Treatment Groups
- Letrozole alone, Letrozole + 40 mg megestrol, Letrozole + 160 mg megestrol
- Key Finding
- Both doses of megestrol slowed tumor growth equally
- Potential Side Effects of Megestrol
- Weight gain, increased blood pressure, hot flashes, shortness of breath, facial swelling, blood clots
- Study Publication
- Nature Cancer