Abstract
A health-conscious lifestyle may protect against breast cancer in situ. However, breast cancer in situ is mainly detected by screening, and many studies lack information on screening participation. Thus, we evaluated the association between prediagnostic lifestyle and risk of breast cancer in situ, accounting for screening participation at recruitment. A score reflecting the adherence to the World Cancer Research Fund/American Institute for Cancer Research cancer prevention recommendations was constructed, using the recommendations on healthy body weight, physical activity, consumption of plant-based foods, red and processed meat, alcohol and avoidance of sugar. Cox proportional hazards regression models were used to investigate the association between the lifestyle score and breast cancer in situ risk, while accounting for important confounders. The lifestyle score was not significantly associated with breast cancer in situ risk (HR(continuous) = 0.96, 95% CI = 0.91-1.03) in the overall cohort. In participants not reporting dietary changes in the past 5 years, the lifestyle score was inversely associated with breast cancer in situ risk (HR(continuous) = 0.92, 95% CI = 0.85-0.99). In those reporting dietary changes in the past 5 years due to illness or other reasons, the lifestyle score was not associated with breast cancer in situ risk (HR(continuous) = 1.04, 95% CI = 0.94-1.15). Lifestyle was inversely associated with breast cancer in situ risk in women not reporting recent changes in their dietary habits. This inverse association is consistent with inverse associations reported in previous studies. Our findings suggest that breast cancer in situ and invasive breast cancer share a similar risk factor profile.