The effect of modifiable risk factors on breast cancer aggressiveness among black and white women

Introduction: Although breast cancer incidence is higher among white women, black women are more likely to have aggressive tumors with less favorable histology, and to have a worse prognosis. Obesity and alcohol consumption have been identified as two modifiable risk factors for breast cancer, while physical activity may offer protection. Little however is known about the association of these factors with race on the severity of breast cancer.

Methods: Data collected as part of a large prospective study looking at insulin resistance and race among women with breast cancer was queried for patient characteristics, lifestyle factors and tumor characteristics. The association with Nottingham Prognostic Index (NPI) was assessed with different models using univariate and multivariate linear regression.

Results: Among 746 women in our cohort, 82% (n = 615) were white and 18% (n = 131) were black, mean age 58 years. Black patients were more likely to have high BMI (31.0 vs. 26.7, p < 0.0001), comorbidities (69% vs 55%, p = 0.01), self-reported poor diet (70% vs 42%, p < 0.001), be sedentary (56% vs 46%, p = 0.03) and were less likely to consume alcohol (8% vs 32%, p < 0.0001) compared to white patients. Overall, 137 (18%) of the patients had poorer prognosis (NPI > 4.4), which was significantly associated with younger age (55.6 vs 58.5 years, p = 0.02), black race (27% vs 15%, p = 0.001), triple negative cancer (15% vs 6%, p = 0.003), and poor diet (54% vs 45%, p = 0.046) compared to patients with better prognosis (NPI ≤ 4.4). On multivariate analysis, (model R² = 0.12; p < 0.001), age (β = -0.011 per year, p = 0.002), healthy diet (β = -0.195, p = 0.02), and exercise (β = -0.004, p = 0.02) were associated with better prognosis, while black race (β = 0.247, p = 0.02) and triple negative cancer (β = 0.908, p < 0.0001) were associated with poor prognosis. Neither alcohol use nor BMI was significantly associated with NPI.

Conclusion: Among modifiable risk factors, diet and exercise are associated with NPI. Unmodifiable factors including race and biologic subtype remain the most important determinants of prognosis.