Women with left-sided breast cancer who underwent radiation therapy had more than double the risk of developing coronary artery disease compared with women with right-sided cancer, a study shows.

US researchers analysed data from 972 women all aged under 55 when diagnosed with breast cancer between 1985 and 2008, none of whom had pre-existing heart disease. 

In the study 466 received right-sided radiation therapy and 506 received left-sided radiation therapy.

With up to 27 years of follow-up, the overall incidence of coronary artery disease was 10.5% for women who received left-sided radiation versus 5.8% for those who received right-sided treatment.