The association between acute myocardial infarction and subsequent diagnosis of breast cancer: a nationwide, population-based cohort study.

Coronary artery disease (CAD) such as acute myocardial infarction (MI) share several common risk factors with cancers, and each disease may influence the prognosis of the other. Recently, acute MI was demonstrated to accelerate the outgrowth of preexisting breast cancer cells but the risk of breast cancer after MI remains unclear. This study aimed to investigate the association between acute MI and a subsequent diagnosis of breast cancer. Female patients with and without a history of acute MI were identified from nationwide databases in Taiwan. Patients with a diagnosis of cancer, MI or CAD prior to the study period were excluded. After reducing confounding through inverse probability of treatment weighting, we compared the incidence of newly diagnosed breast cancer between patients with a history of acute MI and those without. As a result, a total of 66,445 female patients were obtained, including 15,263 patients with a history of acute MI and 51,182 patients without. The incidences of breast cancer during follow-up were 1.93 (95% confidence interval [CI] 1.78-2.09) and 1.80 (95% CI 1.67-1.93) per 1,000 person-years for patients with and without a history of acute MI, respectively. The hazard ratio (HR) was 1.05 (95% CI 0.78-1.41, P = 0.756). In subgroup analysis, breast cancer risk was significantly associated with acute MI in patients using antidiabetic drugs (HR 1.27; 95% CI 1.02-1.58) and in low to moderate urbanization levels (HR 1.28; 95% CI 1.06-1.53). In conclusion, the risk of newly diagnosed breast cancer was not increased in patients with acute MI when compared to general population without MI or CAD.