Do adipokines underlie the association between known risk factors and breast cancer among a cohort of United States women?

Abstract

Introduction: Obesity is a well-established risk factor for postmenopausal breast cancer, but mechanisms underlying the association are unclear. Adipocyte-derived, cytokine-like adipokines have been suggested as contributory factors. To evaluate their association with breast cancer risk factors and breast cancer risk, we conducted a nested case-control study of 234 postmenopausal breast cancer cases and 234 controls in a cohort of U.S. women with prospectively-collected serum samples obtained in the mid 1970s and followed for up to 25 years.

Methods: Adiponectin, absolute plasminogen activator inhibitor-1 (aPAI-1), and resistin were measured by a multiplex immunoassay. Sex hormones were available for 67 cases and 67 controls.

Results: Among controls, we found that lower levels of adiponectin and higher levels of aPAI-1 were correlated with increasing levels of estradiol (Spearman r=-0.26, p-value=0.033; r=0.42, p=0.0003), decreasing levels of sex hormone binding globulin (r=0.38, p=0.0013; r=-0.32, p=0.0076), and increasing body mass index (BMI) (r=-0.31, p=<0.0001; r=0.39, p=<0.0001). Hormones were not associated with resistin. Among the relatively small percentage of women using postmenopausal hormones at the time of blood collection (13.7%), aPAI-1 levels were higher than in non-users (p=0.0054). Breast cancer risk was not associated with circulating levels of adiponectin (age-adjusted p for linear trend=0.43), aPAI-1 (p=0.78), or resistin (p=0.91). The association was not confounded by BMI, parity, age at first full-term birth, age at menopause, current postmenopausal hormone use, and circulating sex steroid hormones. Furthermore, adipokine associations were not modified by BMI (p>0.05). The lack of association with risk may be due to measurement error of the laboratory assays.

Discussion: lower levels of adiponectin and higher levels of aPAI-1 measured in prospectively-collected serum from postmenopausal women were associated with increasing BMI but not breast cancer risk.