Lead researcher, Dr Daniel Rea reported that the "aTTom" study demonstrated that estrogen receptor positive breast cancer patients who took tamoxifen for longer than five years were much less likely to suffer cancer recurrence or die from the disease. Currently, the recommended period for tamoxifen therapy is five years.
The study involved 6,953 adult females with breast cancer. 580 patients from 3,468 women took tamoxifen for ten years, while 672 of 3,485 patients stopped tamoxifen after five years.
Dr Rea reported that:
- 25% of the 10-year tamoxifen patients had fewer recurrences of breast cancer than those on just five years of therapy
- There were 23% fewer deaths in the 10-year tamoxifen group
"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."
About estrogen receptor positive breast cancer and tamoxifenApproximately three-quarters of all breast cancers are of the estrogen receptor positive kind. This type of breast cancer benefits from hormone therapy. Estrogen, a female hormone, encourages breast cancers to grow by activating estrogen receptors. Tamoxifen works by blocking these receptors, thus making it much harder for the cancer to recur after surgery or invade the other breast.
Tamoxifen side effects - patients on tamoxifen may experience menopausal-type symptoms, including hot flashes (UK: hot flushes) and night sweats. A Norwegian study found that acupuncture reduces menopausal symptoms in tamoxifen patients by 50%. More rarely, tamoxifen has also been linked to an increased risk of developing blood clots, endometrial cancer and stroke.
Stroke risk did not rise with 10 years of tamoxifen therapy compared to five years, the researchers found. However, the risk of endometrial cancer did increase. Fortunately, endometrial cancer is usually diagnosed in the early stages of the disease, when it can be treated successfully.
According to the researchers, thirty breast cancer deaths would be prevented for every endometrial cancer death due to long-term tamoxifen therapy.
Professor Richard Gray, who is based at the University of Oxford and was also presenting the aTTom trial 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."
The aTTom trial was funded by the Medical Research Council, UK.
A trial led by Oxford University's Clinical Trial Service Unit reported in The Lancet (December 2012 issue) that taking tamoxifen for ten years after breast cancer surgery is more effective than five years. The study was called ATLAS.
Written by Christian Nordqvist