MONDAY, Feb. 14, 2005 (HealthDayNews) -- Taking the breast cancer drug tamoxifen lowers a woman's risk of heart attack, a new study suggests.

The researchers found that women taking tamoxifen reduced their risk of developing heart disease symptoms by about 40 percent and their risk of heart attack by about 20 percent, compared with those not taking the drug.

Although women who must use tamoxifen can take comfort in the fact that it doesn't cause cardiovascular problems, experts caution it should not be used solely to protect the heart. The report appears in the Feb. 14 online issue of Cancer.

"We found that women taking tamoxifen had a reduced risk of heart attacks or chest pain related to heart disease," said study co-author Dr. James A. Kaye, a research associate at the Boston Collaborative Drug Surveillance Program and an associate professor of epidemiology at Boston University School of Public Health.

Earlier studies have found that women taking tamoxifen have lower levels of cholesterol and homocysteine, both markers for heart disease. But whether tamoxifen could actually be protective wasn't known.

In their study, Kaye's team looked at the medical records of 3,030 women with breast cancer who were taking tamoxifen and compared them with 4,233 other cancer patients not treated with the drug.

Benefits were seen in women who had been taking tamoxifen for less than two years, and continued through the five years of treatment, according to the report.

Kaye suggested the protective effect of tamoxifen might be due to its ability to block estrogen. Estrogen replacement therapy has been linked to an increased risk of heart disease, he noted. "There may be a reversal of the effects of estrogen by tamoxifen, or it may have anti-estrogenic effects itself in relation to heart disease," he said.

"There shouldn't be a concern about an increased risk of heart disease if you are taking tamoxifen for breast cancer. In fact, these data support the opposite view," Kaye said. "We are obviously not supporting the use of tamoxifen to treat heart problems."

Another study in the same journal found that women with hypothyroidism are less likely to develop breast cancer than women without the condition. Hypothyroidism is a common condition in which the thyroid gland doesn't produce normal amounts of thyroid hormone.

"Low thyroid hormone and hormone replacement therapy produce some effect on the breast tissue so that tumor onset is delayed or doesn't come at all," said lead researcher Dr. Massimo Cristofanilli, from the University of Texas M. D. Anderson Cancer Center.

In the study, the researchers compared medical records from 1,136 women with breast cancer with the records of 1,088 healthy women being screened for breast cancer.

Cristofanilli's team found that women with hypothyroidism had a 61 percent lower risk of developing breast cancer compared with women without the condition. In addition, women with breast cancer were 57 percent less likely to have hypothyroidism compared with healthy women.

Moreover, "we found that women with hypothyroidism who happened to have breast cancer had a smaller tumor, more estrogen-dependent disease and less involvement on lymph nodes," Cristofanilli said.

Cristofanilli believes that using this information about thyroid hormone might lead to new ways to treat or prevent breast cancer. "There is a new opportunity for the prevention and treatment of breast cancer," Cristofanilli said. "We think that this is a line of research that needs to be opened."

Debbie Saslow, director of breast and gynecologic cancer at the American Cancer Society, isn't sure that either study adds much to the fight against breast cancer. The tamoxifen study "doesn't have a lot of implications," she said.

The cardiac benefit of tamoxifen is an added plus, Saslow said. "But I don't think that doctors would choose to prescribe tamoxifen based on this potential benefit to the heart," she added. The advantages of tamoxifen against breast cancer so far outweigh these additional benefits that they wouldn't be considered, she explained.

As for the thyroid study, Saslow was also not too impressed with the findings. "It's not going to change anything today, but has some findings that will prompt future research," she said.

"But there are a lot of interesting lines of research," Saslow said. "And how many of them actually have implications for how patients are treated? These things are so far in the future, and so few things come to pass."

More information

The American Cancer Society can tell you more about breast cancer.

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