Myocardial infarction among women with early-stage breast cancer treated with conservative surgery and breast irradiation

Purpose: To assess the possible impact of the irradiation on the risk of acute myocardial infarction among breast cancer patients treated with conservative surgery and postoperative radiation therapy. Methods and Materials: The incidence of and mortality from acute myocardial infarction was assessed in a group of 684 women with early-stage breast cancer diagnosed during 1976-1987 who had been treated with breast conserving surgery plus postoperative radiation therapy given with tangential photon fields. In 94% of the patients the total dose was between 48-52 Gy given with 2 Gy daily fractions 5 days per week for a total treatment period of about 4 (1(2)) - 5 (1(2)) weeks. In 88% of the patients the target volume included the breast parenchyma alone. In the remaining patients regional nodal areas were also irradiated. A concurrent group of 4,996 breast cancer patients treated with mastectomy without postoperative radiation therapy was used as a reference. Results: After a median follow-up of 9 years (range: 5-16 years) 12 conservatively treated patients (1.8%) had developed an acute myocardial infarction and 5 (0.7%) had died due to this disease. The age-adjusted relative hazard of acute myocardial infarction for the conservative group vs. the mastectomy group was 0.6 (95% C.I.: 0.4-1.2) and for death due to this disease 0.4 (0.2-1.1). The incidence of acute myocardial infarction among the conservatively treated women was similar irrespective of tumor laterality. Conclusions: There was no indication of an increased risk of acute myocardial infarction with the radiation therapy among the women treated with conservative surgery. However, due to the small number of events the study could not exclude the possibility that cardiac problems may arise in some patients with left-sided cancers who have their heart located anteriorly in the mediastinum. Individual, three-dimensional dose planning represents one method to identify such patients and is basic to technical changes aimed at decreasing the cardiac radiation dose volume