The United States will experience a 20 percent drop in the breast cancer death rate overall, with about 40,000 women dying of the disease this year, Peto said. 21,000 will die instead of 28,000, he said. Britain is slightly ahead, probably because tamoxifen was invented there and used there first, Peto said. Breast cancer is particularly problematic because remnants may remain after a tumor has been cut out and can cause a recurrence of cancer years later. There are three main treatments after surgery.
Radiotherapy targets the remnants of cancer lurking in or near the breast.
Chemotherapy is a cocktail of cell-killing drugs, and tamoxifen and other hormonal drugs block hormones from nurturing the cancer. Tamoxifen alone has been found to head off one in six recurrences and cut the risk of relapse by more than one-third. It also halves the risk of a new cancer occurring in the other breast, according to Peto's analysis, which examined the largest-ever collection of existing evidence on cancer therapy. While tamoxifen fights cancer, it also can cause womb cancer and blood clots in the lungs. But using the drug for five years does 30 times more good than harm, the study found.