TAKING tamoxifen for 10 rather than five years halves the risk of women dying from the most common kind of breast cancer. This is according to new research being presented at this year’s ASCO conference.
The Cancer Research UK study shows oestrogen receptor positive breast cancer patients taking tamoxifen for longer than the recommended five years are better protected against recurrence and are less likely to die from the disease.
The ‘aTTom’ study looked at some 7,000 women with breast cancer who, after five years of taking tamoxifen, either continued taking the drug for another five years or stopped treatment.
Among women who took tamoxifen for 10 years, 25 per cent fewer had recurrences of breast cancer and 23 per cent fewer died, compared to women who took the drug for only five years.
Dr Daniel Rea, who is the clinical lead researcher based at the University of Birmingham, said: “These results are important as they establish that giving tamoxifen for longer than the current standard of five years significantly cuts the risk of breast cancer returning.
“Doctors are now likely to recommend continuing tamoxifen for an extra five years and this will result in many fewer breast cancer recurrences and breast cancer deaths worldwide. Tamoxifen is cheap and widely available so this could have an immediate impact.”
75% of breast cancers are oestrogen receptor positive and could benefit from hormone therapy. The female sex hormone oestrogen encourages breast cancers to grow by activating oestrogen receptors. Tamoxifen blocks these receptors, thus reducing the chance of breast cancer returning after surgery or developing in the other breast.
Despite the benefits of tamoxifen in preventing breast cancers from returning, it does have side effects. Women taking tamoxifen can experience side effects similar to menopausal symptoms, such as night sweats and hot flushes. Rare but serious side effects of tamoxifen include increased risk of endometrial cancer (cancer of the lining of the uterus), blood clots, and stroke.
In this study no increase in the incidence of stroke was observed with 10 years of tamoxifen therapy, though endometrial cancer risk was higher in this arm. Endometrial cancer is often detected early, when it can often be treated successfully. The researchers estimate that for every endometrial cancer death that occurs as a side effect of long-term tamoxifen, there would be 30 deaths from breast cancer prevented.
Professor Richard Gray, based at the University of Oxford and presenting the aTTom results at ASCO, said: “Five years of tamoxifen is already an excellent treatment but there have been concerns that giving it for longer might not produce extra benefits and could even be harmful. The aTTom study establishes that the benefits of taking tamoxifen for longer greatly outweigh the risks.”
Kate Law, director of clinical research at Cancer Research UK, said: “Large clinical trials like aTTom are vitally important to understand how drugs such as tamoxifen work and how best to use them. We need these sorts of studies so we can be sure the benefits from cancer drugs outweigh the side-effects that they may have.”
And commenting on the findings Dr Julia Wilson, Director of Research at Breakthrough Breast Cancer, said: “These findings are extremely exciting for women who are diagnosed with the most common type of breast cancer.
“The study proved 10 years of taking tamoxifen has a much higher survival rate than the current five years, which is vital in helping us to stop breast cancer coming back and more importantly to help us stop women dying of breast cancer.
“Tamoxifen is a well-established and cheap treatment, which means the guidelines for usage should be easy to amend. We do however encourage all women taking this treatment to speak to their doctor about their individual circumstances as there can be side effects involved.”