The risk of dying from breast cancer has been falling rapidly for the past 15 years mainly because the drugs used to treat the disease have been effective at stopping the cancer from returning, according to a major new analysis.
Although surgery and radiation therapy can seem to wipe out the disease in early-stage breast cancer, undetected cancer cells can remain and unleash a life-threatening recurrence years later.
Studies have shown that drugs given to prevent cancer's return can improve the survival rates five years after diagnosis and that the effects last at least 10 years. Several studies have followed women for 15 years, but no single study has been big enough to reliably show the full scope.
In a review published Friday in The Lancet medical journal, researchers led by scientists at Oxford University in England analyzed the combined evidence from 194 studies involving more than 145,000 women with early stage breast cancer who were treated with drugs that were being tested during the 1980s.
They found that the benefits of these drugs are remarkably persistent 15 years after diagnosis.
The analysis found that where both chemotherapy and hormone therapy were appropriate, the risk of death within 15 years of diagnosis could be cut in half, so that if a 50-year-old woman had a 1-in-5 chance of dying from her cancer, the drugs could bring the risk down to 1 in 10.
For women of any age with hormone-sensitive breast cancer — the most common type — giving tamoxifen for five years reduced the breast cancer death rate over the next 15 years by about one-third.
Dr. Karen Gelmon and colleagues at the British Columbia Cancer Agency in Vancouver, who were not connected with the research, noted, however, that the review analyzed older treatment strategies and did not evaluate newer drugs that are standard therapy today.
The therapies studied in the Lancet paper have been proven, she said, but the next challenge is to cure even more women with newer and more targeted drugs.
However, the work is important in confirming the benefits over time from chemotherapy and hormone treatments, and will be reassuring to doctors and patients, she said.
The review is the fourth analysis to be conducted by the same group of scientists on the largest database of patients for any type of cancer. About 1.15 million new cases of breast cancer are diagnosed every year worldwide.
Earlier reviews assessed the effect of various drugs on recurrence and survival over five and 10 years. The last overview, in 2000, found that better treatments over the preceding decade had slashed breast cancer death rates in Britain and the United States by one-quarter among some groups.