Not only does hormone replacement therapy raise the risk of breast cancer in postmenopausal women, it raises the risk of a specific type of malignancy called lobular breast cancer.
Researchers, reporting in the journal Cancer Epidemiology, Biomarkers and Prevention, also found that the cancer risk appeared earlier than the five-year period cited by other research.
The study is one of the largest to focus on lobular cancer, which accounts for about 15 percent of all cancers.
Ductal cancer is the most common form of breast cancer, accounting for 70 percent of all cases.
Lobular cancer develops in the areas of the breast that contain milk-producing glands and is more likely to be estrogen-receptor positive and therefore responsive to targeted treatments, resulting in an 11 percent lower risk of death when compared with its ductal counterpart.
Ductal cancer develops in the ducts that carry milk from the lobules to the nipple and is more difficult to detect.
"We found that women who were using combined estrogen and progestin hormone therapy had a nearly 300 percent increased risk in their risk of lobular, but only a 40 percent increase in their risk of ductal cancer," says study author Dr. Christopher I. Li.
"There is clear, strong, consistent evidence that using combined estrogen and progestin hormone therapy increases a woman's risk of breast cancer" says Dr. Li, who is at Fred Hutchinson Cancer Research Center in Seattle, Washington.
It is less well known how these hormones influence risk of different types of breast cancer.
"This is basically another confirmation of previous information," adds Dr. Jay Brooks, at Ochsner Health System in Baton Rouge, Louisiana. "People who take combined estrogen and progestin are running a significant risk of cancer and heart disease. They really need to know that."
Others, however, downplayed the results.
Dr. Steven Goldstein, author of The Estrogen Alternative and Could It Be Perimenopause? says, "Nothing in this paper is new as far as I'm concerned.
"It doesn't change the current recommendations which are that we should use hormone therapy in the lowest effective dose; for the shortest period of time possible; and consistent with patient treatment goals with reevaluation periodically," he says.
Previous studies, namely the Women's Health Initiative (WHI), found that combined estrogen and progestin hormone replacement therapy increased the risk of breast cancer in postmenopausal women.
Further studies have indicated that the risk is greater with lobular carcinoma than with ductal carcinoma, but these studies have not been definitive.
The rates of both invasive lobular carcinoma (ILC) and invasive ductal-lobular cancer (IDLC) increased 52 percent and 96 percent, respectively, from 1987 to 1999 in the US.
Invasive ductal carcinoma (IDC) increased only 3 percent during the same period, according to the study.
Since the WHI results were announced in 2003 and 2004, HRT use has declined 38 percent to 68 percent in the US. Nevertheless, some 57 million prescriptions for postmenopausal HRT are still filled each year, according to the study.
Dr. Li looked at more than 1,500 postmenopausal women, 1,044 with breast cancer and 469 in a control group for comparison.
Among the women with breast cancer, 324 had lobular cancer, 196 had mixed ductal-lobular cancer, and 524 had ductal cancer. The women were ages 55 to 74 years and had been diagnosed between 2000 and 2004.
Women currently using combined hormone therapy had a 2.7-fold increased risk of lobular cancer and a 3.3-fold increased risk of mixed ductal-lobular cancer.
The increased risk was seen only in women who had used combined HRT for three or more years.
In women who had mixed cancers, HRT increased the risk of tumors that were primarily lobular but not those that were primarily ductal in nature.
Current use of combined HRT was associated with about double the risk of tumors that were mostly lobular (although this was not considered statistically significant), about a fivefold increased risk of mostly ductal, and a 7.7-fold increased risk in tumors that were mixed in features.
Like the WHI, this study did not show an increased risk of breast cancer in women who were taking estrogen-only hormone therapy, which is only recommended for women who have had a hysterectomy.
Always consult your physician for more information.
Although there are some women who are at higher risk, the fact is all women are at risk for breast cancer.
That is why it is so important to follow the three-step plan for breast health. Early detection of problems provides the greatest possibility of successful treatment.
Some people with one or more risk factors never develop a disease, such as cancer, while others develop cancer and have no known risk factors.
Although certain factors MAY suggest or define a person's possible risks, they do not necessarily cause the disease.
Different diseases, including cancers, have different risk-factor lists.
When reading about risk factors for breast cancer, keep in mind that the word "risk" is used in different ways:
Lifetime risk refers to the probability that a person, over the course of his or her lifetime, will be diagnosed or die from cancer.
Over her lifetime, a woman in the United States has a 1 in 8 risk of developing breast cancer, and a 1 in 33 risk of dying from breast cancer.
Relative risk is a measure of the strength of the relationship between risk factors and cancer.
With respect to breast cancer, it compares the risk of developing breast cancer in women who have a certain trait or exposure to women who do not have the trait or exposure.
About 20 percent to 30 percent of women with breast cancer have a family member with this disease.
Risk factors that cannot be changed:
The most frequently cited lifestyle-related risk factors:
Environmental risk factors including exposure to pesticides, or other chemicals, are currently being examined as a possible risk factor.
Always consult your physician for more information.
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