Aromatase Inhibitor Cardiovascular Risk Characterised

Aromatase inhibitor therapy in stage I–III breast cancer patients may increase the risk of myocardial infarction compared with tamoxifen use

medwireNews: Women with early-stage breast cancer who use aromatase inhibitor (AI) therapy have a higher risk of myocardial infarction (MI) than their counterparts using tamoxifen , although survival remains higher overall, Canadian researchers report.

The baseline prevalence of ischaemic heart disease (IHD) in women aged 55 years and older with a first stage I–III breast cancer diagnosis between 2005 and 2010 was comparable for the 7409 patients who received primary therapy with AIs and the 1941 patients given tamoxifen, at 17.0% versus 16.9%.

But over an average follow-up of 1184 days, 1.4% of the AI-treated patients experienced MI compared with 0.9% of the tamoxifen group, giving a significant hazard ratio (HR) of 2.02 after propensity score analysis to reduce the impact of a raft of confounding factors.

The increased risk of MI was comparable when examining only women aged 66 years and older (HR=2.23) or those with a history of IHD (HR=1.67). Similarly, the HR for MI was 1.53 when assessing a group of patients considered to have a low risk of cardiac events who were aged less than 74 years, with stage I or II breast cancer and no prior IHD.

When choosing adjuvant endocrine therapy, clinicians should consider the increased risk of MI with AI therapy compared with tamoxifen, Geoffrey Anderson, from the Institute for Clinical Evaluative Sciences in Toronto, Ontario, and co-workers therefore recommend.

“It also mandates close attention to risk factor modification and increased suspicion for IHD in aromatase inhibitor-treated women”, they write in the European Journal of Cancer.

Nevertheless, the authors note that overall survival data for the population were in favour of AI therapy, “which likely reflects that most of the early deaths after a diagnosis of breast cancer are due to the malignancy rather than cardiovascular disease or other causes”.

The incidence of death in the AI therapy group during 1202 days of follow-up was 34.7 events per 1000 patient–years versus 43.3 events per 1000 patient–years over 1146 days in patients using tamoxifen, giving a significant HR of 0.83.

Analysis of a composite endpoint of death or MI also favoured AI therapy when considering the whole patient population and subgroups of patients aged 66 years or older and those with prior IHD. And in the low-risk patient group, AI therapy was comparable to tamoxifen for this endpoint.

Acknowledging that their study did not address sequential use of tamoxifen and AIs, the team concludes that further research is required to determine the long-term implications of cardiovascular risk in endocrine therapy users. 


Abdel-Qadir H, Amir E, Fischer HD, et al. The risk of myocardial infarction with aromatase inhibitors relative to tamoxifen in post-menopausal women with early stage breast cancer. Eur J Cancer; 68: 11–21. 30 September 2016. DOI:

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