TORONTO - A new study suggests long-term use of tamoxifen is linked to an increased risk of a second type of breast cancer.
U.S. researchers looked at more than 700 women who had been diagnosed with breast cancer and compared them to nearly 400 diagnosed with both a first and second breast cancer.
Tamoxifen is an estrogen-blocking drug researchers say has been shown to reduce the risk of dying of breast cancer.
Researchers found women who received tamoxifen for five or more years lowered their risk of developing the more common type of breast cancer that responds to estrogen-blocking therapy.
But the study found the risk of another rare subtype of the disease increased by more than 400 per cent.
Lead author Dr. Christopher Li says it's important to remember any treatment has both risks and benefits, and that tamoxifen has been shown to lower the risk of recurrent breast cancer in women.
The study was published online Tuesday in the journal Cancer Research.
