Estrogen Benefit in Breast Cancer Affirmed
Adjusting for nonadherence actually boosted the apparent protective effect to an HR of 0.68, and to HR 0.58 when looking only at the intervention period.
In subgroup analyses, the lower breast cancer incidence with estrogen appeared only in women without history of benign breast disease and those without a mother or sister with breast cancer (P=0.01 and P=0.02 for interaction).
But age, body mass index, years since menopause, and gap between menopause and hormone therapy initiation didn’t significantly impact the effect. Detection bias from mammography differences was unlikely, the researchers noted.
They cautioned though about the small numbers of breast cancer deaths, some attrition for extended follow-up, and the median of only 4.7 years of post-intervention follow-up.
Being overweight or obese
Being overweight or obese has been found to increase breast cancer risk, especially for women after menopause. Before menopause your ovaries produce most of your estrogen, and fat tissue produces a small amount of estrogen. After menopause (when the ovaries stop making estrogen), most of a woman’s estrogen comes from fat tissue. Having more fat tissue after menopause can increase your chance of getting breast cancer by raising estrogen levels. Also, women who are overweight tend to have higher blood insulin levels. Higher insulin levels have also been linked to some cancers, including breast cancer.
But the connection between weight and breast cancer risk is complex. For example, the risk appears to be increased for women who gained weight as an adult but may not be increased among those who have been overweight since childhood. Also, excess fat in the waist area may affect risk more than the same amount of fat in the hips and thighs. Researchers believe that fat cells in various parts of the body have subtle differences that may explain this.
Whether the results could be generalized to lower estrogen doses, other preparations, or longer durations of estrogen use is not known, they added.
But the results do not apply to combination therapy with estrogen and progestin for postmenopausal women who haven’t gone through a hysterectomy. In the other arm of the WHI trial, combination therapy was associated with increased cancer incidence, delayed diagnosis, and higher mortality of breast cancer, the group warned.
What are the risk factors for breast cancer
Simply being a woman is the main risk factor for developing breast cancer. Although women have many more breast cells than men, the main reason they develop more breast cancer is because their breast cells are constantly exposed to the growth-promoting effects of the female hormones estrogen and progesterone. Men can develop breast cancer, but this disease is about 100 times more common among women than men.
“The comparability of breast cancer incidence rates for the placebo groups in the two trials suggests that differences in hormone therapy, rather than hysterectomy, is the primary determinant,” they concluded.
The study was funded by the National Heart, Lung and Blood Institute and Wyeth. The WHI program is funded by the National Heart, Lung and Blood Institute, NIH, and the U.S. Department of Health and Human Services.
Anderson reported having no conflicts of interest. A co-author reported having been a consultant for AstraZeneca, Novartis, Amgen, and Pfizer; receiving funding support from Amgen; and serving on speakers’ bureaus for AstraZeneca and Novartis.
Howell and Cuzick reported having no conflicts of interest.
###
Primary source: Lancet Oncology
Source reference: Anderson GL, et al “Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women’s Health Initiative randomised placebo-controlled trial” Lancet Oncol 2012; DOI:10.1016/S1470-2045(12)70075-X.