According to scientists, hundreds of thousands of women with breast cancer could potentially benefit from having a low-cost female hormone added to their therapy.
A study found during research in animals that the hormone, progesterone, slowed the growth of breast cancers when it was combined with tamoxifen, the standard drug treatment.
About 1.7 million women are diagnosed with breast cancer annually around the world. About half of these women could benefit from progesterone therapy if the findings are confirmed in clinical trials.
According to researchers, in the United Kingdom alone, every year about 25,000 women have breast tumors that could respond to this new therapy.
The results are clear and potentially have direct benefits for many women with breast cancer.
For while doctors have been aware that levels of certain molecules in breast tumors have an impact on how well the cancer will respond to treatment. Women whose tumors have high levels of oestrogen receptor benefit from drugs that block the effects of the oestrogen hormone.
The drugs are able to work because they put a brake on the cell division and tumor growth driven by oestrogen.
However, until now, experts were unaware of why the progesterone receptor, another molecule, is also important. Women that have breast cancers with high levels of both oestrogen and progesterone receptors, have the best survival rates.
Researchers found that adding progesterone to double positive cancers, along with tamoxifen, slowed their growth more than the drug alone.
When progesterone sticks to the progesterone receptor in cancer cells, it alters how the oestrogen receptor works and effectively puts a second brake on tumor growth. Test demonstrated that mice given progesterone and tamoxifen had breast tumors only have the size of those given the drug on its own.
These findings provide a strong case for a clinical trial to investigate the potential benefit of adding progesterone to drugs that target the oestrogen receptor, which could improve treatment for the majority of hormone-driven breast cancers.