Association between Obesity, Race or Ethnicity, and Luminal Subtypes of Breast Cancer

Abstract

Luminal breast cancers are the most common genomic subtype of breast cancers where Luminal A cancers have a better prognosis than Luminal B. Exposure to sex steroids and inflammatory status due to obesity are key contributors of Luminal tumor development. In this study, 1928 patients with Luminal A breast cancer and 1610 patients with Luminal B breast cancer were compared based on body mass index (BMI), age, race, menopausal status, and expressed receptors (i.e., estrogen (ER), progesterone (PR), and human epidermal growth factor receptor 2 (HER2)). Patients with Luminal B tumors had a significantly higher mean BMI (Δ = 0.69 kgm−2 [0.17, 1.21], p = 0.010) versus Luminal A. Interestingly, the risks of Luminal B tumors were higher among Black/African American patients versus White and Hispanic patients (p < 0.001 and p = 0.001, respectively). When controlled for each other, Black/African American race (p < 0.001) and increased BMI (p = 0.008) were associated with increased risks of Luminal B carcinoma, while postmenopausal status was associated with a decreased risk (p = 0.028). Increased BMI partially mediated the strong association between Black/African American race and the risk of Luminal B carcinoma. Thus, Black/African American race along with obesity seem to be associated with an increased risk of more aggressive Luminal B breast carcinomas.

Keywords: Luminal A; Luminal B; breast cancer; obesity; race.

Figure 1

Model diagrams (A,C) and sensitivity plots (B,D) of the mediation analyses examining whether the association between Black/African American race and Luminal B breast carcinoma is mediated by BMI before (A,B) and after (C,D) controlling for the menopausal status. ACME, average causal mediation effect; ADE, average direct effect; a, regression coefficient between Black/African American race and BMI; b, regression coefficient between BMI and Luminal B cancer when controlled for Black/African American race; c, regression coefficient between Black/African American race and Luminal B cancer; c’, regression coefficient between Black/African American race and Luminal B cancer when controlled for BMI; τ, sensitivity parameter required to nullify ACME. Confidence intervals have been obtained using a non-parametric bootstrap approach (1000 simulations). Light colored arrows arising from the covariate Menopause represent the regression coefficients between Menopause and each outcome variable (i.e., BMI and Luminal B cancer) in each model.