Reproductive and hormonal factors may pose more risk for some types of breast cancer than others, according to research published online Aug. 25 in Cancer.
Amanda I. Phipps, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues analyzed data from two pooled case-control studies of women aged 55 to 79, which included 1,023 cases of luminal breast cancer, 39 cases of HER-2 overexpressing breast cancer, 78 cases of triple-negative cancer, and 1,476 controls.
Early menarche (under the age of 13) was associated with higher risk of HER-2-overexpressing cancer (odds ratio, 2.7), and late menopause and estrogen/progestin therapy were associated with higher risk of luminal disease (ORs, 1.6 and 1.7, respectively), the report indicates. Luminal tumors are typically marked by expression of estrogen receptor-α and progesterone receptors. Breastfeeding for at least 6 months was linked to lower risk of luminal and triple-negative disease (ORs, 0.8 and 0.5), the researchers note.
“Although definitive conclusions regarding which risk factors are more strongly related to certain molecularly defined subtypes of breast cancer cannot be made based on the current study, our data do support the premise that risk factor profiles vary by breast cancer subtype and that hormonal risk factors have a greater impact on luminal-type breast cancers than HER-2-overexpressing or triple-negative tumors. The observation that breastfeeding has now been shown to reduce the risk of triple-negative disease in two studies is intriguing, but the biologic basis for this association is unclear and this finding requires further replication,” the authors write.
Phipps AI, Malone KE, Porter PL, et al. Reproductive and hormonal risk factors for postmenopausal luminal, HER-2-overexpressing, and triple-negative breast cancer. Cancer. 2008;113:1521-1526.