Researchers suggest women switch drugs to treat breast cancer

A drug called anastrozole is better at preventing relapses among certain breast-cancer patients than tamoxifen, the current standard treatment, according to new research presented at a medical conference Wednesday.

The study’s authors suggest that postmenopausal women whose tumors grow in response to hormones should take anastrozole, also known by the brand name Arimidex, rather than tamoxifen. Women already taking tamoxifen may want to switch, according to the study’s researchers, who presented their findings at the San Antonio Breast Cancer Symposium.

Other cancer experts say that it’s too soon to eliminate tamoxifen, noting that doctors don’t know the long-term effects of anastrozole, which belongs to a class of drugs called aromatase inhibitors.

Tamoxifen, also known by the brand name Nolvadex, works by blocking the action of estrogen, which can feed certain types of breast tumors.

Tamoxifen eventually stops working, however, allowing cancers to grow back.

That’s why doctors typically prescribe tamoxifen for five years before switching to aromatase inhibitors, which prevent the body from making estrogen. Relapsed breast cancer is usually fatal.

In this trial, doctors studied nearly 9,400 breast cancer patients for five years, giving some anastrozole and others tamoxifen, according to the study, also published online in the British medical journal, The Lancet. Compared with tamoxifen – which cuts the risk of cancer recurrence by 50 percent – anastrozole reduced the chance of relapse by 70 percent to 80 percent, according to the study.

AstraZeneca, which makes both drugs, paid for the trial. Its patent for tamoxifen has expired, company spokeswoman Mary Lynn Carver says.

Cancer experts say that tamoxifen remains the standard in premenopausal women. Aromatase inhibitors only work in women whose bodies do not produce estrogen.

Researchers say it’s too soon to tell whether women who took aromatase inhibitors for this study are surviving longer than those on tamoxifen.

Tests of tamoxifen took seven years to show that the drug helped women live longer.

The American Society of Clinical Oncology recommended last month that most postmenopausal breast-cancer patients take aromatase inhibitors. But it did not rule out combining them with tamoxifen.

Doctors don’t yet know which works best: taking aromatase inhibitors alone, or taking them after five years of tamoxifen, says Eric Winer, director of breast cancer at the Dana-Farber Cancer Institute and chairman of the ASCO panel that wrote the new recommendations.

“With tamoxifen, it took us well over a decade before we understood all the side effects,” Winer says. “We have to be really careful that we don’t rush to judgment.”