Chance of second breast tumor linked to long-term tamoxifen use

A new study suggests long-term use of tamoxifen is linked to an increased risk of a second type of breast cancer.

US 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. The US study links use of the drug to a four-fold raised risk of developing a more aggressive, difficult-to-treat tumor, not dependent on estrogen.

Tamoxifen, developed by UK drug major AstraZeneca but now off patent, 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.  However, this latest study found the risk of another rare subtype of the disease increased by more than 400%. The study was published on-line in the journal Cancer Research on August 25.

Lead researcher Christopher Li said: "It is clear that estrogen-blocking drugs like tamoxifen have important clinical benefits and have led to major improvements in breast cancer survival rates. However, these therapies have risks, and an increased risk of ER negative (estrogen receptor negative) second cancer may be one of them. Still, the benefits of this therapy are well established and doctors should continue to recommend hormonal therapy for breast cancer patients who can benefit from it."

Jack Cuzick, head of Cancer Research UK's Centre for Epidemiology, Mathematics and Statistics at Queen Mary, University of London, reported by the UK public broadcaster the BBC, stressed that tamoxifen had a proven track record.

He said: "There is overwhelming evidence that tamoxifen, and newer more effective hormone blocking treatments, prevent far more recurrences, new breast cancers and cancer-related deaths than they might stimulate." Prof Cuzick said some of the non-hormone sensitive tumours recorded in the study may have started out as hormone-sensitive, but had been kept at bay by tamoxifen treatment.