Introduction Population-attributable risk estimation of modifiable postmenopausal breast cancer risk factors might help to guide public health initiatives.
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 ORs and population attributable risks (PARs) for modifiable and non-modifiable risk factors. We examined overall postmenopausal invasive breast cancer as well as tumour subtypes by estrogen receptor (ER) and progesterone receptor (PR) status.
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 to 47.2%) regarding overall invasive tumours, and 36.5% (23.3 to 47.6%) regarding ER+/PR+ tumours. 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 to 23.2%) and 12.8% (5.5 to 20.8%), respectively, regarding overall invasive tumours. For ER+/PR+ tumours, the corresponding PARs were 25.3% (20.9 to 29.7%) and 16.6% (7.0 to 26.0%). The summary PARs (95% CIs) for HT use and physical inactivity together were 29.8% (21.8 to 36.9%) and 37.9% (30.6 to 46.2%) regarding overall invasive and ER+/PR+ tumours, respectively.
Conclusions The population-level impact of modifiable risk factors appears to be comparable to that of non-modifiable risk factors. Alterating the prevalence of 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+ tumours, the most frequently diagnosed subtype.