Cardiovascular Risk From Radiotherapy Higher in Patients With Prior MI


SAN ANTONIO — A history of MI in women who subsequently develop breast cancer sharply increases 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 diagnosed with right-sided breast cancer.

Cancer sidedness is a key element of RACE because most radiotherapy regimens—particularly those popular until the early 1980s—direct a larger dose of ionizing radiation to the heart when applied to the left breast, noted Dr. Darby, professor of medical statistics at University of Oxford (England).

Further cross-checking of the Scandinavian national registries revealed 2,244 subjects had a fatal or nonfatal MI after being diagnosed with breast 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.

The story was very different 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 modest increase didn't reach statistical significance, it was of similar magnitude as the increase in risk Dr. Darby found in an earlier study, which did achieve significance because of greater patient numbers (Lancet Oncol. 2005;8:557–65).

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