Long-term tamoxifen may increase risk

SEATTLE, Aug. 26 (UPI) -- The hormone tamoxifen decreases breast cancer survivors' risk of one cancer, but may increase risk for another cancer type, U.S. researchers said.

Dr. Christopher Li and colleagues at Fred Hutchinson Cancer Research Center in Seattle said hormonal therapy with drugs like tamoxifen is one of the most common treatments for breast cancer survivors because it has been shown to reduce the risk of dying from the most common, less aggressive type of second breast cancer.

The researchers compared breast-cancer patients who received the estrogen-blocking drug tamoxifen to those who did not.

The study assessed history of tamoxifen use among 1,103 breast cancer survivors from the Seattle area who were initially diagnosed with estrogen receptor-positive breast cancer between the ages of 40 and 79. Of these, 369 of the women developed a second breast cancer.

The study, published in the journal Cancer Research, found while the drug was associated with a 60 percent reduction in estrogen receptor-positive second breast cancer -- the more common type, which is responsive to estrogen-blocking therapy -- it also appeared to increase the risk of estrogen receptor-negative second cancer by 440 percent.

"This is of concern, given the poorer prognosis of estrogen receptor-negative tumors, which are also more difficult to treat," Li said in a statement.