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.