Breast-Feeding, Other Factors, May Affect Risk of Breast Cancer Type

Factors such as age at menopause and a woman’s breast-feeding practices can influence her risk of developing certain types of breast cancer. That was the conclusion of a new study to be published in the October 1, 2008, issue of CANCER. The study’s results suggest that there are distinct and separate hormonal risk factors associated with different subtypes of breast cancer.

Amanda Phipps, a predoctoral research associate at the Fred Hutchinson Cancer Research Center in Seattle, and her colleagues conducted a study to better understand the specific risk factors for the subtypes of breast cancer, which are classified by expression of the estrogen receptor, the progesterone receptor, and the HER2 receptor. The research team suspected that reproductive or hormonal factors may play a significant role in a woman’s risk of developing different subtypes because these cell receptors are influenced by endogenous sex hormones.

The scientists pooled two population-based studies of breast cancer in women aged 55 to 79 years. Their analysis included 1,023 women with breast cancer whose cells express the estrogen and progesterone receptors (luminal cancers), 39 women with HER2-overexpressing breast cancer, and 78 triple-negative cases (no expression of estrogen, progesterone, or HER2 receptors). The study also included 1,476 women without breast cancer.

Risk Factors Varied by Subtype

The investigators found that reproductive risk factors varied considerably by breast cancer subtype. For example, early age at menarche was associated with risk of HER2-overexpressing disease but not with any other subtype. Breast-feeding for 6 months or longer was associated with a lower risk of luminal cancer as well as triple-negative cancer. Both late age at menopause and use of estrogen plus progestin hormonal therapy were associated with an increased risk of luminal disease. Finally, no differences in risks associated with number of children or the age when a woman first gave birth were observed by subtype.

The study authors concluded that their results indicate that “certain reproductive factors may have a greater impact on risk of certain molecular subtypes of disease compared to others.”