A large international study confirms the drug tamoxifen protects women at high risk from getting breast cancer, although the benefits may not be as great as earlier reports suggest.
For about four years, the study followed more than 7,000 healthy women with a higher than normal chance of developing breast cancer. The results show tamoxifen prevented cancer in about 35 percent, said Jack Cuzick, who heads an international group that presented the findings this week at the European Breast Cancer Conference.
"There are still issues as to whether the benefit is worth the side effects," said Cuzick, head of mathematics, statistics and epidemiology at Cancer Research UK in London.
For that reason, the international group is not ready to join American scientists in recommending tamoxifen to healthy women for breast cancer prevention.
In the case of women who have breast cancer, there is universal agreement that tamoxifen is worth the side effects for warding off a cancer recurrence.
American researchers concluded in 1998 that tamoxifen should be recommended for women at high risk of getting breast cancer because a U.S. study showed the drug prevented the disease in about half the women who took it.
Tamoxifen works by blocking the action of the female hormone estrogen, which fuels the growth of breast cancer in about 75 percent of cases.
The most serious side effect is that tamoxifen doubles or triples the chances of a life-threatening blood clot. It also doubles the risk of cancer of the lining of the womb.