CHICAGO--New drug cocktails have shown promise in the fight against breast cancer, a diseases that annually kills more than half an million of women around the world, two new studies show.

The research was unveiled at an annual meeting here of the American Society of Clinical Oncology.

One of the large-scale studies that involved 1,800 women showed that a treatment against osteoporosis that uses the biophosphate Zometa has shown to reduce the risk of early breast cancer in pre-menopausal women by 35 percent.

Zometa, which is produced by Swiss pharmaceutical giant Novartis, contains zoledronic acid.

This category of medicine is already being used against bone metastasis -- the spread of cancer to the bones -- and osteoporosis, a disease that leads to bone loss.

"It's very exciting to find that in addition to preventing bone loss in women undergoing adjuvant endocrine therapy for breast cancer, zoledronic acid can also reduce the likelihood that breast cancer will return in some women," said Michael Gnant, a professor at the Medical University of Vienna.

"This large clinical trial demonstrates that the anti-tumor activity of adjuvant zoledronic acid improves outcomes beyond the effect of endocrine therapy alone," Gnant said at a press conference.

"Future research will focus on optimizing the administration schedule and the dose, and determining which patients will benefit the most from treatment with zoledronic acid," Gnant added.

If a second round of clinical tests confirms the results, oncologists believe that Zometa could be used to fight other types of cancer that present high risks of bone metastasis, such as kidney cancer.

Meanwhile, another international clinical study indicated that a treatment combining Avastin, which stems the blood supply to tumors, with cell division blocker Taxotere slows the progression of advanced breast cancer.

In earlier studies, Avastin (a trade name for the drug bevacizumab) added to Taxol (paclitaxel) -- similar to Taxotere (docetaxel) -- doubled the survival rate of women with advanced breast cancer that had metastasized.

Taxol and Taxotere are used in chemotherapy.

The phase-three study -- the last step before a treatment can be marketed -- is the first in the United States to evaluate Avastin-Taxotere, which is used in Europe, Asia and Australia, while the US has been combining Avastin with Taxol.

The study, headed by David Miles, professor and medical oncologist at the Mount Vernon Cancer Center, involved 736 women in 24 countries for one year.

It found tumor reduction in 44.4 percent of patients treated with Taxotere and a placebo, against 55.2 percent for those treated with Taxotere and a small dose of Avastin, and 63.1 percent for those treated with Taxotere and a high dose of Avastin.

"This study shows the antiangiongenic approach to treating breast cancer is effective, regardless of which taxane drug it is combined with," said Miles.

"We found it does not add a great deal of toxicity of chemotherapy, which should be reassuring to physicians recommending this course of treatment," he added.

Avastin is sold by Swiss laboratory Roche and US pharmaceutical Genentech. In 2007, the companies sold $2.3 billion worth of the product.

An estimated 184,450 new cases of breast cancer will be registered in the United States this year, and 40,930 will likely have a fatal outcome.

The disease kills about 502,000 women a year worldwide, according to 2005 figures released by the World Health Organizations.