Associations of Post-Diagnosis Lifestyle with Prognosis in Women with Invasive Breast Cancer

Background: Lifestyle habits can impact breast cancer develop-ment, but its impact on breast cancer prognosis remains unclear. We investigated associations of post-diagnosis lifestyle with mor-tality and recurrence in 1,964 women with invasive breast cancer enrolled in the Kaiser Permanente Northern California Pathways Study shortly after diagnosis with lifestyle information at baseline (2005-2013) and the 2-year follow-up. Methods: We calculated a post-diagnosis lifestyle score (range, 0-18) based on 9 diet, physical activity, and body weight recom-mendations from the American Cancer Society/American Society of Clinical Oncology (ACS/ASCO) using follow-up data (body weight also included baseline data); higher scores indicate greater guideline concordance. Similarly, we calculated a pre-diagnosis lifestyle score using baseline data to investigate pre-to post -diagnosis changes. We estimated hazard ratios (HR) and 95% confidence intervals (CI) using Cox proportional hazard models, with follow-up through December 2018 (observing 290 deaths and 176 recurrences). Results: The 2-year post-diagnosis lifestyle score was inversely associated with all-cause mortality (ACM; HR per 2-point increase 1/4 0.90; 95% CI, 0.82-0.98), and breast cancer-related mortality (HR, 0.79; 95% CI, 0.67-0.95), but not recurrence. Relative to women who maintained low concordance with recommendations at both time points, women who maintained high concordance had a lower risk of ACM (HR, 0.61, 95% CI, 0.37-1.03). Improved concordance with some specific recommendations (particularly PA) may be associated with a lower hazard of ACM (HRPA, 0.52; 95% CI, 0.35-0.78). Conclusions: Results suggest that women with breast cancer may benefit from a post-diagnosis lifestyle aligned with ACS/ASCO guidelines. Impact: This information may potentially guide lifestyle recom-mendations for breast cancer survivors to reduce mortality risk.