Prior MI Boosts Radiotherapy's Cardiac Risk in Breast Ca Patients


SAN ANTONIO — A history of MI in women who later develop breast cancer doubles their risk of radiotherapy-induced MI, Sarah Darby, Ph.D., reported at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.

She presented an update from the ongoing observational Radiation-Associated Cardiac Events (RACE) study involving nearly 63,000 Danish and Swedish patients diagnosed with early-stage breast cancer during the late 1970s through the beginning of the current decade.

By cross-referencing RACE participants against Danish and Swedish national hospital registries, investigators determined 1.1% of the women had an MI prior to their diagnosis of breast cancer. A history of previous MI was equally common in the 32,485 women with left-sided breast cancer and the 30,468 with right-sided cancer, said Dr. Darby, professor of medical statistics at University of Oxford (England). Of those women, 2,244 had a fatal or nonfatal MI after being diagnosed with cancer. Of those, 41% had undergone radiotherapy.

Nonirradiated patients had a similar risk of subsequent MI regardless of whether they had cancer of the left or right breast. This was true whether or not they had a history of MI prior to breast cancer.

However, in women who underwent adjuvant radiotherapy, those with a previous history of MI had a 2.1-fold greater rate of MI after breast cancer if they had left-sided as opposed to right-sided cancer.

Irradiated women with no history of MI had a 12% greater risk of MI after breast cancer with left-sided disease, compared with right-sided. Although this didn't reach statistical significance, it was of similar magnitude as the radiotherapy-associated cardiac mortality risk Dr. Darby found in an earlier study of more than 300,000 women with early-stage breast cancer in the U.S. Surveillance, Epidemiology, and End Results registry, where the increased risk did achieve significance because of greater patient numbers.

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