TUESDAY, Feb. 19, 2002 (HealthDayNews) -- Breast cancer patients using the drug tamoxifen to protect against recurrence of the disease should not look to extend that protection with the medication raloxifene.
According to research that appears tomorrow in the Journal of the National Cancer Institute, raloxifene did not prevent tumor growth in laboratory mice, and it appeared to increase their risk of endometrial cancer, or cancer of the uterine lining.
"We were trying to do in the laboratory what may never be done in the clinic, and that is give a guesstimate if tamoxifen followed by raloxifene was going to be good or bad. And the answer is, it is bad," says study author V. Craig Jordan, professor of cancer research at Northwestern University and the scientist who developed tamoxifen.
Both drugs are known as SERMs -- short for selective estrogen receptor modulators. They are frequently referred to as "designer estrogens" because they offer some of the positive effects of this hormone without many of the drawbacks.
They are known to work by interfering with the actions of estrogen that is produced naturally in the body. By blocking certain actions, particularly in the breast, where hormone-sensitive cancers can develop, SERMS are thought to reduce the risk of breast cancer, particularly in those women at highest risk.
Indeed, tamoxifen has been the primary treatment for preventing the recurrence of breast cancer in women who've already had at least one bout with the disease.
Although the drug creates a slight risk of endometrial cancer, its breast cancer-preventive qualities are still thought to far outweigh its risks.
"We knew that taking tamoxifen for one to two years was better than not taking it at all, and that taking it for five years was better than one to two years," says Dr. Clifford Hudis, chief of the Breast Cancer Medicine Service at Memorial Sloan-Kettering Cancer Center.
However, studies show that taking tamoxifen beyond five years does not offer any additional protection from breast cancer. As doctors began searching for other drugs that could continue to offer patients that "security blanket," raloxifene came to mind.
As an estrogen-like compound used to treat osteoporosis, studies show it does not appear to increase the risk of either breast or uterine cancer. So, many believed it might be the logical choice to follow tamoxifen therapy.
"But we didn't have any studies to show how it would respond in these women -- the ones who had already used tamoxifen -- which is why our research became necessary," Jordan explains.
The new study involved hundreds of mice that were implanted with cells with endometrial and breast cancer.
The mice were treated with tamoxifen for the human equivalent of five years, along with low-dose estrogen, enough to mimic the amount a post-menopausal woman would produce naturally.
When the tamoxifen therapy ended, the mice began treatment with raloxifene, and their incidence of cancer was recorded.
The Northwestern scientists found raloxifene did not prevent the growth of breast tumors previously exposed to tamoxifen, and it did not block the growth of estrogen-sensitive cancers in the uterus.
In short, the study authors conclude that raloxifene offers no protection beyond what tamoxifen provides.
"Once you are exposed to tamoxifen, giving raloxifene afterwards really changes the pharmacology of raloxifene, so it becomes just like putting more tamoxifen in the body," Jordan says.
For Hudis, the study is an important verification of what doctors already suspected.
"In essence, from a purely conservative clinical point of view, this data tells us to keep on not doing what we should not have been doing anyway," Hudis says.
He calls the study "consistent with what we see clinically from this class of drugs," and adds that "from the cancer point of view, there is less difference between these drugs than one might have hoped."
In an accompanying editorial, Dr. Michael B. Sporn of Dartmouth Medical School points out that what the study does not show is whether raloxifene might help prevent the development of "second primary breast cancer or primary endometrial cancer."
However, these questions may be answered by the National Cancer Institute's STAR trial, which will include more than 20,000 women. A head-to-head comparison of raloxifene and tamoxifen as the primary treatment for the prevention of breast cancer in women at greatest risk, it is expected to yield results within several years.
Meanwhile, both Jordan and Hudis reiterate that the cancer-causing effects of raloxifene seen in this latest study would likely only be seen in women who have breast cancer and take the drug following five years of tamoxifen therapy.
They add that women using raloxifene for the treatment of osteoporosis should not be concerned with the study results at this time.
What To Do
To learn more about tamoxifen therapy for breast cancer, visit The National Cancer Institute.
Go here to learn more about the STAR trial.
To learn more about how breast cancer develops and recurs, visit The National Alliance of Breast Cancer Organizations.
For the latest information on raloxifene as treatment for osteoporosis, check out The National Osteoporosis Foundation.
