| To identify more homogeneous subgroups of breast cancer for evaluating risks associated with hormone-related exposures, estrogen receptor/progesterone receptor (ER/PR) status and/or Her2/neu oncogene amplification were used to subdivide breast cancer patients. Data were from the Carolina Breast Cancer Study (CBCS), a population-based, case-control study of 889 invasive breast cancer cases aged 20 to 74 years and 841 controls frequency-matched on race and age. ER and PR status were abstracted from medical records. Her2/neu amplification was determined by differential polymerase chain reaction on paraffin-embedded breast tissue retrieved from the hospitals. Information on risk factors was obtained by personal interview. Hormone-related factors, such as early age at menarche, nulliparity, late age at first full-term pregnancy, body mass index, waist-hip ratio, and oral contraceptive use, were found to be statistically significantly associated with increased risks for breast cancer positive for ER and PR, especially after stratification by menopausal status, with odds ratios (ORs) ranging from 1.6 to 2.3. In contrast, some factors for which the relevance of hormones is less clear showed elevated risks for breast cancer negative for ER and PR, especially among non-postmenopausal women, with ORs ranging from 1.6 to 2.0. The interaction between Her2/neu amplification and hormonal exposures, however, was not shown as consistently. Increased risks for breast cancer positive for Her2/neu amplification (Her2+) were found for alcohol drinking and medical radiation to the chest (ORs: 2.1-2.3 for non-postmenopausal women), in addition to nulliparity and late age at first full-term pregnancy (ORs: 1.9-2.4 for postmenopausal women). Long lactation showed decreased risk for Her2+ breast cancer (OR: 0.2 for postmenopausal women). Combining the two sets of biomarkers helped better discriminate risks between breast cancer subtypes for some risk factors. Nevertheless, the observed patterns were not particularly distinct or interpretable, and they were based on small numbers. These results suggest that ER/PR, and to a lesser extent Her2/neu, may be critical loci through which hormone-related factors influence risk of breast cancer. |
