Nikhil Prasad Fact checked by:Thailand Medical News Team Jan 06, 2026 1 day, 10 hours, 31 minutes ago
Medical News: A widely used drug long-prescribed to ease hot flashes in women undergoing breast cancer treatment may also help slow the cancer itself. New research led by scientists in the United Kingdom has revealed that megestrol, when added to standard hormone therapy, may offer a double benefit by reducing treatment side effects while directly lowering tumor growth.
Low dose megestrol may both ease hot flashes and slow tumor growth in hormone driven breast cancer
This discovery could improve both comfort and long-term outcomes for thousands of women living with hormone sensitive breast cancer.
A common type of breast cancer
Around three quarters of all breast cancers are known as estrogen receptor positive. This means the cancer cells rely on estrogen in the body to grow and multiply. To stop this, doctors often prescribe anti estrogen drugs such as letrozole. These medicines lower estrogen levels and are usually taken for many years.
While effective, these treatments can cause uncomfortable menopause like symptoms such as hot flashes joint pain fatigue and bone thinning. Because of this, some women struggle to continue treatment for the recommended length of time.
An old drug with a new role
Megestrol acetate is a man-made form of the hormone progesterone. For years, low doses of megestrol have been used to reduce hot flashes caused by anti-estrogen therapies. Now researchers believe it may do more than just improve comfort.
According to this
Medical News report, the drug may also directly slow the growth of estrogen driven breast cancer when combined with standard therapy.
How the study was carried out
The findings come from the PIONEER clinical trial led by researchers from the University of Cambridge. The study involved 198 postmenopausal women with early-stage estrogen receptor positive breast cancer.
Participants were recruited from 10 hospitals across the United Kingdom including Addenbrooke’s Hospital in Cambridge. They were divided into three groups. One group received the anti-estrogen drug letrozole alone. The second group received letrozole plus a low daily dose of megestrol at 40 milligrams. The third group received letrozole with a higher megestrol dose of 160 milligrams.
The treatment lasted for two weeks before surgery to remove the tumor. Researchers then compared tumor samples taken before and after treatment.
Clear reduction in tumor activity
The study showed that women who received megestrol alongside letrozole had a greater reduction in tumor cell growth compared to those who received letrozole alone. Importantly, the lower 40 milligram dose worked just as well as the higher dose.
This was measured using a marker called Ki67 which indicates how quickly cancer cells are dividing. Lower Ki67 levels are linked to better long-term outcomes in breast cancer.
g>Why progesterone matters
Laboratory studies conducted by the Cancer Research UK Cambridge Institute helped explain these results. Scientists found that progesterone and drugs like megestrol interfere with estrogen signaling inside cancer cells. In simple terms, progesterone changes how estrogen behaves, making it harder for cancer cells to grow.
When progesterone or megestrol was added to anti-estrogen treatment in lab models, tumor growth slowed even further.
Safety and side effects
Another encouraging finding was safety. High doses of megestrol are already approved for use in advanced breast cancer but can cause weight gain high blood pressure and blood clots if used long term.
In this trial, the lower dose caused fewer side effects and showed no increase in serious complications such as dangerous blood clots or high blood pressure. This makes low dose megestrol a more attractive option for long term use.
What this means for patients
The findings suggest that adding low dose megestrol to standard hormone therapy could both ease hot flashes and directly suppress cancer growth. Because megestrol is off patent, it is also inexpensive and widely available, making it accessible even in lower resource healthcare settings.
Conclusion
This study highlights a promising and practical approach to improving breast cancer care. By combining megestrol with existing hormone treatments, patients may benefit from better cancer control improved quality of life and higher chances of staying on treatment long term. While larger and longer studies are still needed, these results open the door to a simple and affordable strategy that could meaningfully change everyday clinical practice.
The study findings were published in the peer reviewed journal: Nature Cancer.
https://www.nature.com/articles/s43018-025-01087-x
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https://www.thailandmedical.news/articles/cancer
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