(CNN) -- A new combination of treatments can help battle some forms of metastatic breast cancer and slow down the spread of the disease, according to two separate studies.
The new studies show that the combinations of treatments significantly overcome or reduce drug resistance in the metastatic phase. That phase is when the cancer has spread beyond the breasts and lymph nodes, doctors said.
Results from the two clinical trials also revealed combining two targeted therapies can slow the progression of the cancer. Scientists presented the research at the San Antonio Breast Cancer Symposium on Wednesday in Texas.
About 200,000 women are diagnosed with breast cancer a year, according to Dr. Ben Ho Park, an associate professor of oncology at Johns Hopkins University School of Medicine.
"These two studies address about 80% of breast cancers in the metastatic setting," said Park, who is not involved in the trials.
In one trial -- BOLERO-2 -- researchers found postmenopausal women with advanced "hormone receptor-positive breast cancer" did better when they took combination therapies rather than a single hormonal treatment.
Women in the trial took a combination of a hormone blocking drug called Aromasin along with a kidney cancer drug called Afinitor, which blocks another signal path inside the cancer cell that tells it to proliferate.
"More patients die of hormone receptor-positive breast cancer than other types of breast cancer," said Dr. Gabriel Hortobagyi, one of the study's authors and chairman of the department of breast medical oncology at the University of Texas in Houston.
Women with hormone receptor-positive breast cancer are given hormone blocking drugs like Tamoxifen (for pre-and postmenopausal patients), blocking estrogen activity in the breast or other aromatase inhibitors (in postmenopausal women), which stop the production of estrogen.
But cancer cells have the ability to get around these hormone-blocking drugs and find ways to make tumors grow again like activating a protein called mTOR, which promotes cell growth and division.
In this trial, 724 women, whose cancer had become resistant to aromatase inhibitors Femara and Arimidex, were given the aromatase inhibitor Aromasin plus placebo or Aromasin plus Afinitor, an approved kidney cancer drug that blocks the mTOR protein.
While it is too early to determine whether this drug combination helps women live longer, Hortobagyi says it determined that for women taking Afinitor, the cancer stopped growing in a higher proportion of patients and for a longer period of time than in women getting the placebo.
After one year, researchers found women getting Aromasin plus Afinitor had on average 7.4 months of progression-free survival -- more than doubling progression free survival - compared to women in who only took Aromasin and a placebo.
The other trial, known as CLEOPATRA, looked at preventing drug resistance in a type of breast cancer where tumor growth is driven by a protein called Her-2/neu, which is found in about 25% of breast cancers.
A drug called herceptin directly attacks the protein and shuts down cancer growth, which makes pairing it with chemotherapy more effective, doctors said.
But cancer cells can figure out a way around treatments too.
In the CLEOPATRA trial, 808 women were given standard therapy plus placebo or standard therapy plus an experimental drug pertuzumab, which binds to a different part of the Her2 protein.
The median progression-free survival for women getting standard therapy was 12.4 months; in women also taking pertuzumab, the cancer didn't start to grow again until six months later on average.
"This is huge. It is very uncommon to have a clinical trial show this level of improvement in progression-free survival," lead researcher Dr. Jose Baselga said in a news release.
Both studies only measured progression-free survival, but Park cautions the gold standard for determining the benefit of a cancer drug is overall survival.
Is the patient living longer because of the treatment? He says early studies for another Genentech cancer drug called Avastin showed a benefit in progression-free survival and the FDA approved its use for breast cancer patients.
But after more studies didn't show women were living longer after taking Avastin, the FDA withdrew its approval for breast cancer last month (it's still approved for other cancers).
CLEOPATRA results were presented at the conference Wednesday and published in the New England Journal of Medicine. Genentech applied for FDA drug approval and its parent company Roche submitted an application to the Europe's counterpart to the FDA, the European Medicines Agency, according to the company.
Both drugs used in the BOLERO trial are FDA approved, so doctors could prescribe the kidney cancer Afinitor to treat breast cancer, which is called "off-label" use.
But it's unclear whether doctors will be prescribing this right away.
"Oncologists are familiar with this drug and know it's available, said Dr. Vered Stearns, co-director of the breast cancer program at Johns Hopkins University School of Medicine.
Results of the BOLERO trial are promising, Stearns said, adding that she's not sure whether this treatment will be readily available in the near future because "many insurance companies ask for the diagnosis as well." Afinitor is only approved for kidney cancer and kidney transplants, according to Stearns, so the question becomes whether the insurance companies will pay for prescriptions for breast cancer treatment.
"l don't how easy it is to write a prescription and get it paid for," she said.