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(NBC NEWS) -- Researchers say they can add a new option to the toolkit for womenwho want to lower their risk of breast cancer - a pill calledanastrozole.

A study released on Thursday shows that the pill,which is available generically, lowered the risk of breast cancer by 53percent in women at high risk of the disease. That's a little bitbetter than the other drugs now being used to prevent breast cancer,such as tamoxifen. And women taking anastrozole had fewer side-effects,the researchers told the San Antonio Breast Cancer symposium.

"Theefficacy is clearly better and we think the side-effects are betterthan tamoxifen," said Dr. Jack Cuzick of King's College London, who ledthe study. "There had been lots of concern about aches and pains. Now wecan say most of them have nothing to do with the drug."

Thefindings, also published in the Lancet medical journal, add to the listof choices available to women considered at high risk of breast cancer.Tamoxifen was the first drug shown to not only treat breast cancer, butto prevent it in women at high risk. Since then two others have beenadded to the list. Anastrozole could be the fourth.

All the pillshave side-effects, some of them unpleasant. They can include hot flashesand blood clots. Tamoxifen and a related drug, raloxifene, canstrengthen the bones but the so-called aromatase inhibitors can causeaches and pains and may weaken the bones.

Aromatase inhibitorsinclude anastrozole, sold generically and under the brand name Arimidex;exemestane, made under the brand name Aromasin; and Femara or etrozole.They're used to treat breast cancer and to prevent it coming back inwomen who have had it once. Exemestane can also be used to preventbreast cancer in women who have never had it but who have a high riskand the new study shows anastrozole can, too.

Studies have shownthat women who took tamoxifen for five years were 50 percent less likelyto have their cancer return and the aromatase inhibitors have similareffects. But if a breast cancer patient has not gone through menopause,tamoxifen is the only safe hormone-based drug to take.

Breast cancer is the second-biggest cancer killer of America women,after lung cancer. The American Cancer Society says 232,340 cases willbe diagnosed in 2013, and more than 39,000 people will die of breastcancer this year. Separately on Thursday, the World HealthOrganization's International Agency for Research on Cancer reported asharp rise in breast cancer globally.

It reported that 1.7 millionwomen around the world were diagnosed with breast cancer globally, a 20percent increase since 2008. Death rates have risen 14 percent.

"Breast cancer is also a leading cause of cancer death in the lessdeveloped countries of the world. This is partly because a shift inlifestyles is causing an increase in incidence, and partly becauseclinical advances to combat the disease are not reaching women living inthese regions," says Dr. David Forman, who led the data gatheringeffort at IARC.

The study released on Thursday is the firstrandomized trial to examine anastrozole specifically. It included morethan 3,800 women past menopause and aged 40-70 from 18 countries.

Womenwere considered at high risk of breast cancer if they had two or moreblood relatives with breast cancer, a mother or sister who developedbreast cancer before age 50, or a mother or sister who had breast cancerin both breasts, or had certain high-risk types of benign breastdisease.

Half were given an anastrozole pill and half got a dummypill to take every day for five years. After five years, 2.8 percent ofthe women who took the drug got breast cancer, compared to 5.6 percentof those taking a placebo.

The drug prevented so-called hormonereceptor positive cancers - those affected by estrogen. It didn't havean effect on the rate of other types of breast cancer, especiallyso-called triple negative breast cancer. It also reduced a type ofpre-cancer called ductal carcinoma in situ (DCIS), Cuzick's teamreported.

"The reported reductions are larger than are thosereported for tamoxifen or raloxifene. Therefore, anastrozole is anattractive option for postmenopausal women at increased risk of breastcancer," they wrote.

Women who took placebo were no more likely todie of their breast cancer than women who got anastrozole, perhapsbecause all the women got annual mammograms and other careful checks.Any that developed tumors were treated right away.

Dr. CliffordHudis, a breast cancer expert at Memorial Sloan-Kettering Cancer Centerand president of the American Socity for Clinical Oncology, says becauseanastrozole is available generically it should be cheaper too

"It'simportant because it's another tool," he says. "It's a widely availabletool that's been given to million of people and has a proven safetyrecord." Women with fragile bones should stick to raloxifene, however,he said. The aromatase inhibitors turn estrogen all the way off andthat's not good for everyone.

Raloxifene, an osteoporosis drug sold under the brand name Evista, can also prevent breast cancer but it can cause blood clots.

Cuzicksays women in some trials of aromatase inhibitor drugs complained aboutaches and pains. In his trial, 58 percent of the women taking placeboscomplained of aches and pains, compared to 64 percent takinganastrozole. Women getting the real drug did have much higher rates ofhot flashes and dry eyes, however.

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