The types of chemotherapy and hormonal therapy that have long been used to help prevent breast cancer recurrence have much greater effects on 15-year than on 5-year survival, according to a study involving researchers from Oxford's Clinical Trial Service Unit and published in this week's issue of The Lancet. This is one of the main reasons why breast cancer death rates have been falling rapidly ever since the early 1990s in the UK and USA.
In early breast cancer, surgery (or surgery and radiotherapy) can appear to remove all traces of the disease, but undetected deposits of cancer cells may remain that could, over the next 5, 10 or 15 years, develop into a life-threatening recurrence. Chemotherapy and/or hormonal therapy are often given as additional treatments in early breast cancer to help prevent recurrence, and can improve 5-year survival.
The Early Breast Cancer Trialists' Collaborative Group coordinated the world's largest collaborative analysis of cancer trials, bringing together data from 145,000 women with early breast cancer in 194 randomised trials. The study includes information on various treatments that were being tested in the 1980s, and have since been widely used, such as 6 months of anthracycline-based chemotherapy (in which an anthracycline is combined with two older drugs, fluorouracil and cyclophosphamide) and 5 years of tamoxifen.
The investigators found that where both chemotherapy and hormonal therapy are appropriate they can approximately halve the 15-year risk of death from breast cancer. For example, if a 50-year-old women had a one in 5 risk of dying from her hormone-sensitive breast cancer, then this risk could be halved, to about one in 10. For middle-aged women with breast cancer, 6 months of anthracycline-based chemotherapy reduces the breast cancer death rate over the next 10 or 15 years by about one third. For women of any age with hormone-sensitive early breast cancer, the commonest form of the disease, 5 years of tamoxifen also reduces the breast cancer death rate over the next 10 or 15 years by about one third. For middle-aged women with hormone-sensitive disease, a combination of both of these treatments halves the breast cancer death rate. The researchers note that while chemotherapy and tamoxifen can have unpleasant short-term side-effects, any long-term side effects are much smaller than the long-term survival benefits.
Professor Sarah Darby of the CTSU, who helped coordinate the collaboration, said: 'For middle-aged women with hormone-sensitive breast cancer, six months of anthracycline-based chemotherapy and five years of tamoxifen halves the long-term risk of death from the disease. Such treatments have been used widely for several years and were endorsed by a US consensus panel in 2001. Although newer treatments are now gaining favour, the eventual long-term benefits from older treatments such as these are one of the main reasons why breast cancer mortality rates are now falling rapidly in countries such as the UK or USA.'
She added: 'This is the largest analysis of randomised evidence ever done in any type of cancer. Because so many women in previous decades agreed to join these randomised trials, millions of women in future decades will benefit.'
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