The drug recently lost approval for advanced breast cancer, but new studies in Germany and the U.S. suggest it might help women with early-stage breast cancer.
In one of the studies, more than one-third of women given Avastin in addition to chemotherapy showed no sign of cancer in their breasts a few months later.
Just 28 percent of women treated with chemotherapy alone had the same result.
In another study, more than 18 percent of patients on Avastin plus chemotherapy had no cancer in their breasts or lymph nodes versus 15 percent of those on chemotherapy alone.
However, researchers emphasize that the true test is whether Avastin improves survival, and it's too soon to know that since both studies are still tracking the women's health.
These were the first big tests of Avastin for early breast cancer, and doctors are cautiously excited about the results.
Avastin is still on the market for some colon, lung, kidney and brain tumors. In 2008, it won conditional U.S. approval for advanced breast cancer because it seemed to slow the disease. Further research showed it didn't meaningfully extend life and could cause heart problems, bleeding and other problems. The government revoked its approval for breast cancer in November.
Doctors can still prescribe Avastin for breast cancer but insurers may not cover it. Treatments can cost $10,000 per month. The drug is still approved for treating advanced breast cancer in Europe and Japan.
The Associated Press contributed to this report.