New research suggests that the breast cancer drug tamoxifen may raise the risk of an aggressive, difficult-to-treat tumour in the other breast.
Dr Christopher Li and colleagues at the Fred Hutchinson Cancer Research Centre, Seattle, Washington, USA, explain that hormonal therapy with drugs like tamoxifen reduces recurrence of less aggressive breast cancer, but may bring a four-fold increased risk of more aggressive secondary cancer.
Using figures on 1,103 breast cancer survivors, they found that tamoxifen was linked with a 60 per cent reduction in oestrogen receptor-positive second breast cancer, but it appeared to increase the risk of oestrogen receptor-negative second cancer by 440 per cent.
Details are published in the journal Cancer Research. Dr Li says: "This is of concern, given the poorer prognosis of oestrogen receptor-negative tumours, which are also more difficult to treat."
These results are more reliable than the team’s earlier study, showing a similar result. "The current study is larger, is based on much more detailed data, and is the first study specifically designed to determine whether tamoxifen use among breast cancer survivors influences their risk of different types of second breast cancers," Dr Li said.
But the findings do not imply that breast cancer survivors should stop taking hormone therapy to prevent a second cancer, he added. "It is clear that oestrogen-blocking drugs like tamoxifen have important clinical benefits and have led to major improvements in breast cancer survival rates.
"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."
Li, C. I. et al. Adjuvant Hormonal Therapy for Breast Cancer and Risk of Hormone Receptor-Specific Subtypes of Contralateral Breast Cancer. Cancer Research, published online August 25, 2009.
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