Population attributable risk of invasive postmenopausal breast cancer and breast cancer subtypes for modifiable and non-modifiable risk factors

BackgroundThe population-level impact of modifiable postmenopausal breast cancer risk factors is incompletely understood, especially regarding potential heterogeneity by estrogen receptor (ER) and progesterone receptor (PR) status.MethodsUsing data on 3074 cases and 6386 controls from a population-based case–control study of postmenopausal breast cancer conducted in Germany between 2002 and 2005, we calculated multivariable-adjusted odds ratios and population attributable risks (PARs) for modifiable and non-modifiable risk factors. We examined overall postmenopausal invasive breast cancer as well as tumor ER/PR subtypes. A bootstrap method provided estimates of 95% confidence intervals (95%CIs).ResultsThe summary PARs (95%CIs) for non-modifiable risk factors (age at menarche, age at menopause, parity, benign breast disease, and family history of breast cancer) were 37.2% (27.1–47.2%) regarding overall invasive tumors, 36.5% (23.3–47.6%) regarding ER+/PR+ tumors, 47.9% (26.4–64.4%) regarding ER+/PR− tumors, and 31.1% (4.0–51.9%) regarding ER−/PR− tumors. Of the modifiable risk factors (hormone therapy (HT) use, physical inactivity, BMI, alcohol consumption), HT use and physical inactivity had the highest impact with PARs of 19.4% (15.9–23.2%) and 12.8% (5.5–20.8%), respectively, regarding overall invasive tumors. For ER+/PR+ tumors, the corresponding PARs were 25.3% (20.9–29.7%) and 16.6% (7.0–26.0%). The summary PARs (95%CIs) for HT use and physical inactivity together were 29.8% (21.8–36.9%) and 37.9% (30.6–46.2%) regarding overall invasive and ER+/PR+ tumors, respectively.ConclusionsThe population-level impact of modifiable risk factors appears to be comparable to that of non-modifiable risk factors. Alterations in HT use and physical inactivity could potentially reduce postmenopausal invasive breast cancer incidence in Germany by nearly 30%, with the largest potential for reduction among ER+/PR+ tumors, the most frequently diagnosed subtype.