Background: The 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.
Methods: Using 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).
Results: The 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.
Conclusions: The 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.
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