|
 |
Long-term use of combined hormones doubles risk
Source: (cancerfacts.com)
Tuesday, June 24, 2003
SEATTLE – June 24, 2003 – Older women who take hormones for more than five years after menopause face a 100 percent increased risk of breast cancer, according to a new study.
The study, led by Dr. Christopher Li of Fred Hutchinson Cancer Research Center found that the increased risk occurred regardless of the method of administration used for the combined estrogen and progestin regimen.
The study, found that women over age 65 who take combined HRT either sequentially (estrogen daily plus progestin about 10 days a month to mimic natural hormonal fluctuations) or continuously (estrogen and progestin daily) for five to 15 years or for 15 or more both face a 100 percent increase in breast-cancer risk. The study appears in the June 25 issue of the Journal of the American Medical Association.
"We found that long-term use of combined estrogen and progestin hormone replacement therapy not only doubles cancer risk, but that the magnitude of this risk increases with duration of use," Li said in a prepared statement.
More than 2,000 older women throughout western Washington participated in the study; half had a history of breast cancer and half did not. Those with a history of breast cancer were diagnosed between 1997 and 1999 and were identified through Fred Hutchinson's Cancer Surveillance System, a population-based registry of cancer incidence in western Washington.
"Focusing exclusively on older women who were diagnosed in more recent years resulted in a relatively high prevalence of HRT use for a long duration," Li said. "This provided us with greater statistical power to measure the link between long-term HRT use and the risks of breast cancer."
The study, funded by the National Cancer Institute, was designed to help researchers understand the causes of breast cancer among women ages 65 to 79 - a group that accounts for more than a third of newly diagnosed breast cancers in the United States. In addition to hormone use, other factors studied included lifestyle, genetics, medication use, and medical and reproductive history.
Among the women with a history of combined HRT use, the majority - 70 percent - took both estrogen and progestin daily (continuous progestin) and 30 percent took progestin about 10 days a month in addition to daily estrogen (sequential progestin).
While the health risks of continuous-combined HRT were publicized widely last summer with the early closing of an arm of the Women's Health Initiative - the effect of sequential-combined HRT on breast-cancer risk until now has been largely undocumented, Li said.
"Few studies have assessed whether sequential progestin use is related to breast-cancer risk, although some studies have suggested that continuous use of progestin is more strongly associated with breast-cancer risk than sequential use," Li said. "In this study we found that both regimens were associated with similar increases in breast-cancer risk. There does not seem to be any advantage to sequential progestin use compared to continuous progestin use with respect to reducing this risk."
In addition to assessing the impact of combined HRT on overall breast-cancer risk, the researchers looked at its effect on the risk of specific types of breast cancer. Among their most significant findings:
Ductal breast cancer - the researchers found a 50 percent increased risk of invasive ductal carcinoma, which accounts for about 80 percent of all breast-cancer cases. This type of breast cancer involves the milk ducts that carry milk from the lobules to the nipple.
Hormone-receptor-positive breast cancer - women who took combined HRT had double the risk of hormone-receptor-positive breast cancer (tumors that need estrogen or progesterone to grow). About two-thirds of all breast cancers are estrogen-receptor positive (ER positive) and progesterone-receptor positive (PR positive). Such tumors respond well to drugs such as tamoxifen that block the effect of estrogen.
Lobular breast cancer - the researchers found a 170 percent increased risk of invasive lobular breast cancer. Lobular carcinoma, the second most common type of breast cancer, involves the chambers in the breast that contain the milk-producing glands. Lobular cancer accounts for 10 percent to 15 percent of cases. The incidence of this type of breast cancer is on the rise nationally; rates have increased 65 percent during the past 12 years (as shown in a study by Li and colleagues published in the March 19, 2003 issue of JAMA).
"The increased use of combined HRT during the past several years may partly account for this rise in lobular breast-cancer rates in the United States," Li said.
Combined HRT did not, however, increase the risk for ER- or PR-negative breast tumors. Because such cancers can grow without estrogen and prostesterone, they are unresponsive to hormonal blockers (like tamoxifen) and more difficult to treat than hormone-receptor-positive tumors.
A potential clinical implication of these findings, Li said, is the need for developing chemotherapeutic agents that target progesterone receptors similar to how tamoxifen is used to treat estrogen receptor positive tumors by blocking the estrogen pathway.
In addition to assessing breast-cancer risk associated with various regimens of combined HRT, the researchers looked at the long-term impact of unopposed estrogen (estrogen-only) on breast-cancer risk. Li and colleagues found that older women who took unopposed estrogen exclusively, even for 25 or more years, were at no greater risk of breast cancer than those who had never taken any form of hormone-replacement therapy.
Copyright © 2001, 2002, 2003 NexCura, Inc. All rights reserved. Republication or redistribution of cancerfacts.com content, including by framing or similar means, is expressly prohibited without the prior written consent of NexCura. NexCura® is a registered trademark and cancerfacts.com™ is a trademark of NexCura, Inc. or its affiliates. Copyright © 2001, 2002, 2003. All rights reserved. This information is for educational purposes only.
|
|
|
|
|
|
