New class of breast cancer drugs look promising

5 June, 2004
 

TOKYO — A new class of breast cancer drugs, called armotase inhibitors, which are used to prevent the growth of estrogen-sensitive tumors, are showing promise for treating the deadly disease.

AIs help prevent the growth of these tumors by lowering the amount of estrogen in the body. It is believed that estrogen-sensitive tumors are responsible for 60 percent of all breast cancer cases.

The gold standard for breast cancer treatment — tamoxifen — which has been used for years, also helps prevent the growth of estrogen-sensitive breast tumors.

But it works differently from AIs. Whereas AIs reduce the amount of estrogen in the body, tamoxifen blocks a tumor's ability to use estrogen.

Some specialists say AIs are producing better results than tamoxifen.

"Studies of tamoxifen, which has been used since the 1970s, has shown it can suppress a recurrence of breast cancer in 50 percent to 70% of patients taking it for five years after operations," said professor Toru Watanabe at the clinical medical research center of the International University of Health and Welfare and head of the Sanno Medical Plaza Oncology Center in Tokyo's Minato Ward.

But studies have show that relapses rise among patients who take tamoxifen for more than five years, and therefore its use has been limited to that time period.

Estrogen is produced by the ovaries and other tissues in the body, using a substance called aromatase.

AIs do not block estrogen production by the ovaries, but they can block other tissues from making this hormone.

That is why they are used mostly in women who have reached menopause, when ovaries are no longer producing estrogen.

AIs when used together with tamoxifen have been shown to be very effective in preventing relapses, Watanabe said.

Three AIs are now available in the United States — anastrazole (Arimidex), exemestane (Aromasin), and letrozole (Femara). But only anastrazole is available in Japan.

More than one study has shown that AIs are effective in preventing relapses. While Watanabe said they need to be further evaluated, he noted that the data so for show a promising outlook for the future. (Kyodo News)