A new study claims that breast cancer patients taking tamoxifen will find that switching to an aromatase inhibitor within three years significantly improves survival rates.

The study, published in the March 15 issue of Cancer and led by Prof Francesco Boccardo, of the National Cancer Research Institute and the University of Genoa in Italy, pooled data from two studies comparing five-year treatment with tamoxifen alone (415 women) or tamoxifen for two to three years followed by an aromatase inhibitor for the remaining treatment period (413 women).

The data showed that compared to treatment with tamoxifen alone, all cause mortality risk and breast cancer-related mortality risk both fell significantly for women switching to an aromatase inhibitor. In addition, there was no increased risk of death from other causes in women who were prescribed the aromatase inhibitor.

Tamoxifen was the first estrogen modulator shown to increase survival and reduce the risk of breast cancer recurrence, note the researchers, but it is associated with increased risk of death from other causes, such as strokes and endometrial cancer. Despite this risk, tamoxifen, which is sold as Nolvadex by AstraZeneca although there are several generic versions on the market and another drug in this class, Eli Lilly’s Evista (raloxifene), “remain an extensively used and popular treatment.”

Aromatase inhibitors, such as AstraZeneca’s Arimidex (anastrozole), work in a different way to lower estrogen levels and the study’s authors say recent evidence shows the latter used alone or in follow-up after two years of tamoxifen therapy “demonstrates clear and, in some cases, improved reduction of recurrence risk.” However, they acknowledge that “there is conflicting evidence about mortality benefits.”

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