The gold standard for treating breast cancer which has held sway for 20 years is expected to change following results showing that death rates can be slashed further by extending drug therapy for longer.
Women who took the drug tamoxifen for ten years rather than the usual five halved their risk of dying from the disease, researchers have found.
Adding an extra five years of treatment cut the risk of dying by a further 25pc, doctors say.
Tamoxifen, discovered in the 1960s, has transformed the treatment of breast cancer and is a key cause of the near 50pc fall in death rates in the last 30 years. There are one million women taking the drug worldwide.
It works by preventing oestrogen being taken up by breast cells where it can be used to fuel cancer. It is long since out of patent, and therefore inexpensive , and is used for treating oestrogen positive breast cancer, the most common sort, which accounts for three quarters of all cases.
But until recently it had been thought that five years of treatment with the drug was enough and longer treatment might carry extra risks.
Now a study of 7,000 women led by the University of Birmingham has confirmed that those who took tamoxifen for a decade had 23pc fewer recurrences of their cancer and a 25pc lower risk of dying than those who stopped treatment after five years.
The aTTom (adjuvant Tamoxifen – To offer more?) study follows publication of the Atlas trial six months ago by the University of Oxford involving over 12,000 women which reached similar conclusions. Taken together the results from the two studies, and accumulating evidence worldwide, are likely to change medical practice.
Dr Daniel Rea, clinical lead researcher from the University of Birmingham, said: “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.”
Like all drugs, tamoxifen has side effects causing some women to experience menopausal symptoms such as night sweats and hot flushes. It also has rare but more serious effects increasing the risk of endometrial cancer (of the lining of the womb) blood clots and stroke.
In this study, funded by Cancer Research UK researchers found an increase in endometrial cancer. But because it is often detected early when it can be successfully treated they estimated that for every endometrial cancer death caused by tamoxifen the drug would prevent 30 breast cancer deaths. There was no increase in stroke in the study.
Professor Richard Gray from the University of Oxford who presented the results at the American Society for Clinical Oncology meeting in Chicago, 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. This study establishes that the benefits of taking it for longer greatly outweigh the risks.”
The benefits of the drug depend on women sticking to the course throughout the ten years of treatment. A study in Scotland found only half of women prescribed tamoxifen or similar drugs for breast cancer were still taking them at the end of five years with some stopping and some reducing the dose.