Earlier large research studies have shown that using hormone replacement therapy (HRT) increases breast cancer risk. The large study reviewed here confirms the earlier results and offers more information on when risk increases, how different types of HRT affect risk, and how HRT affects the risk of different types of breast cancer.
Almost 68,000 post-menopausal women between the ages of 50 and 74 participated in this study, called the Cancer Prevention Study. The study started in 1992. The women's medical histories, including any HRT use and any breast cancer diagnoses, were kept track of for 13 years (until 2005). About half the women (47.6%) never used HRT. The other half either used HRT before enrolling in the study or used HRT at some point during the study. Some of these women used combination HRT (which contains estrogen and progesterone) and other women used estrogen-only HRT.
About 2,300 of the women were diagnosed with invasive breast cancer during the study. The researchers compared the number of women who used HRT and were diagnosed with breast cancer to the number of women who didn't use HRT and were diagnosed. The researchers also analyzed how different types of HRT and how long HRT was used affected risk. Combination HRT and estrogen-only HRT affected breast cancer risk differently.
Combination HRT:
Estrogen-only HRT:
Menopausal side effects can dramatically reduce quality of life for some women. These women have to weigh the benefits of HRT against the risks. If you're having severe hot flashes or other menopausal side effects and are considering HRT, talk to your doctor about all of your options. Ask how you can minimize your breast cancer risk AND relieve your symptoms. Be sure to discuss the pros and cons of different types of HRT. The study reviewed here strongly suggests that estrogen-only HRT appears to increase breast cancer risk less than combination HRT. If you do decide to take HRT, ask if you can take a lower-dose formula and try to take it for the shortest time possible.
Learn more about more about menopause and ways to manage side effects in the Breastcancer.org Managing Menopausal Symptoms section.
ATLANTA, Feb. 2 (MedPage Today) -- The first two to three years of hormone therapy appear to be the most dangerous and the combination of estrogen and progesterone is the regimen most likely to be the source of that danger, researchers here said.
Postmenopausal women who take estrogen plus progesterone face a 75% increased risk for invasive ductal breast cancer and more than a doubling of the risk for lobular breast cancer compared with their peers who don't take hormones, according to Eugenia E. Calle, Ph.D., of the department of epidemiology and surveillance research at the American Cancer Society, and colleagues.
The increased risks "attenuated two years after cessation," the researchers reported online in the March 1 issue of Cancer.
They also found that among women who used unopposed estrogen, there was no overall increase in the risk of invasive ductal cancer, although there was an increased risk among lean women.
There was also an increased risk for distant or regional ductal cancers among estrogen-only users, but the researchers cautioned that this might be a chance finding since it was not supported by evidence from other studies.
And although estrogen-only formulations appeared to be a safer choice than estrogen-progesterone hormone replacement regimens, women who used estrogen for 10 years or longer had a 50% increase in risk of invasive lobular cancer, they wrote.
A number of studies have linked hormone use with increased risk of breast cancer, but Dr. Calle said that few studies have investigated temporal associations between use and increased risk to determine "when risk begins to rise and potentially identify a 'safe' period of time for hormone use."
"Our results show a window of two to three years for the risks of [estrogen plus progesterone] both to become apparent after initial use and to attenuate after cessation of use," she concluded.
The findings were based on an analysis of data from a prospective cohort of 67,754 postmenopausal women enrolled in the Cancer Prevention Study II Nutrition Cohort, which is a prospective study of cancer incidence in 184,000 U.S. adults living in 21 states.
The women were ages 50 to 74 in 1992 and were followed until June 30, 2005.
During follow-up there were 1,821 cases of invasive ductal cancer and 471 cases of invasive lobular or mixed lobular cancer diagnosed.
At baseline 47.6% had never used hormone replacement therapy, 21.2% were users of estrogen only, and 13% were users of estrogen plus progesterone. Additionally, 14.6% were former users of estrogen and 3.6% were former users of estrogen plus progesterone.
In general, current hormone users were leaner, better educated, and more likely to have had a recent mammogram than women who never used hormones. Not surprisingly, estrogen only users were more likely to have had hysterectomies.
"A positive dose-response relation with increased duration of use was observed for ductal cancer (1-<5 years, RR of 1.46 [95% CI 1.19-1.80]; and for ? 10 years of use: RR of 2.07 [95% CI 1.70-2.52])," they wrote.
But for "lobular cancer, the approximate doubling of risk with use of [estrogen plus progesterone] appeared within the first five years of use and did not increase appreciably with longer durations of use."
Hormone use was self-reported, which was a limitation of the study, the authors wrote. Another limitation was the study population, which was mostly white, middle-class, educated women.
Dr. Calle made no disclosures and listed no funding source for the study.
Primary source: Cancer Source reference: Calle EE et al "Postmenopausal Hormone Use and Breast Cancer Associations Differ by Hormone Regimen and Histologic Subtype" Cancer 2009; 115:000-000
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