Using the cancer drug Herceptin before surgery could reduce the number of mastectomies needed in women with breast cancer, scientists say.
Herceptin is used to treat women with HER-2 positive breast cancer
A study showed using the drug with chemotherapy before surgery completely eradicated tumours in 43% of patients with HER-2 positive breast cancer.
This was almost twice as many as for patients treated only with chemotherapy - 23% of these showed the same effect.
The findings were reported to the American Society for Clinical Oncology.
Herceptin is currently used after surgery in women with HER-2 positive breast cancer to prevent tumours returning.
About a quarter of the 44,000 breast cancer patients in the UK each year have HER-2 positive tumours, which are particularly aggressive and likely to return.
Normally women with large tumours are treated with chemotherapy to shrink the tumours so that operations can be performed with less risk of having to remove the whole breast.
In the new research scientists studied 228 patients with HER-2 positive breast cancer.
115 patients received chemotherapy plus Herceptin for one year, and 113 patients received chemotherapy alone, before surgery.
Taking Herceptin made the shrinking more likely, as well as eradicating the tumours completely in many cases.
In 38% pf patients tumours which had spread to other parts of the body were also removed.
Professor Alex Markham, Cancer Research UK's senior medical advisor, said it was encouraging that the cancer was eradicated from the lymph nodes of some patients.
He said the results of the study were exciting, but he added that it had only included a relatively small number of patients.
Dr Andrew Wardley, consultant medical oncologist at Christie Hospital, Manchester, said the results added to the already substantial evidence supporting the use of Herceptin.
He said: "This is very welcome news for patients with a particularly aggressive form of breast cancer, some of whom will no longer face the prospect of losing their breasts."
He added that treating cancer early with Herceptin to eradicate it could have important implications for long-term survival.
The research was carried out by cancer organisation Group SOLTI, and drug manufacturer Roche.