According to results recently published in the Journal of the National Cancer Institute, treatment with chemotherapy or hormone therapy for original breast cancer significantly reduces the long-term risk of developing breast cancer in the contralateral (opposite) breast.

Standard treatment for patients diagnosed with breast cancer typically includes chemotherapy and/or hormone therapy. Hormone therapy is used for patients with hormone-positive breast cancer, which is stimulated to grow from exposure to the circulating female hormones estrogen and/or progesterone. These two types of therapies are systemic, meaning that they circulate throughout the body and can kill cancer cells that have spread from the site of origin.

Patients initially diagnosed with breast cancer have an increased risk of developing cancer in the contralateral breast. However, results from previous studies have indicated that treatment with chemotherapy and/or hormone therapy reduces the risk of contralateral breast cancer. There is limited information, however, on how long risk is reduced and how menopausal status and age impact this risk.

Researchers from Europe and the United States recently conducted a study to help explain the reduction in risk of contralateral breast cancer among women treated with chemotherapy or hormone therapy. This study included data from 1,158 women diagnosed with breast cancer in one breast (control group) and 634 patients diagnosed with contralateral breast cancer. Women in these studies were 55 years of age or younger when initially diagnosed. Diagnoses occurred between 1985 and 1999.

  • Patients treated with chemotherapy had a greater than 40% reduced risk of developing contralateral breast cancer compared with those not treated with chemotherapy.
  • Patients treated with tamoxifen (Novladex®), a hormone agent, had an approximately 34% lower risk of developing contralateral breast cancer than those who did not receive tamoxifen.
  • Risk was reduced among women treated with chemotherapy for 10 years following their initial breast cancer diagnosis. This reduction was greater among women who became postmenopausal within one year of their first breast cancer diagnosis.
  • Women treated with tamoxifen maintained a risk reduction for five years following initial breast cancer diagnosis.

The researchers concluded: “The associations between chemotherapy and tamoxifen treatment and reduced risk for contralateral breast cancer appear to continue for 10 and 5 years, respectively, after the initial breast cancer is diagnosed.”

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Reference: Bertelsen L, Bernstein L, Olsen J, et al. Effect of systemic adjuvant treatment on risk for contralateral breast cancer in the women’s environment, cancer and radiation epidemiology study. Journal of National Cancer Institute. 2008; 100:32-40.

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