Henson KE, et al. - Considering the necessity of information on large numbers of women with breast cancer treated both before and after 1990 to investigate the evidence concerning the selection of women for different adjuvant treatments, and whether any such selection is linked to age at cancer diagnosis or the laterality of cancer, researchers here examined individual patient information from cancer registries and other organizations around the world to render further insight on adjuvant therapies for breast cancer and subsequent heart disease. They here analyzed individual patient data for 1,934,248 women with breast cancer in 22 countries for cardiac mortality; of these, 1,018,505 women were reported as irradiated, 223,077 as undergoing chemotherapy, 317,619 as taking endocrine therapy, and 55,264 died of cardiac disease. The median date of diagnosis was 1996 and the interquartile range was 1987–2002. They observed patient-selection effects for all three treatments. During selection, laterality was also considered for radiotherapy in women irradiated 1990 or later. Before 1990, no such selection was evident in patients irradiated and higher cardiac mortality was noted in left-sided than right-sided cancer. Younger women exhibited greater left-vs-right cardiac mortality rate ratios (1.46, 1.19, 1.20, 1.09, and 1.08 following cancer diagnoses at ages < 40, 40–49, 50–59, 60–69, and 70+ years); the relative increase in cardiac mortality lasted into the third decade following exposure and was greater when chemotherapy was also given.