A new breast cancer drug can halt the growth of cancer by as much as 5 months, while reducing chances of side-effects, according to a report by a team from Guy's Hospital in London.

The treatment, for women with HER2-positive breast cancer - a dangerous disease that attacks as many as 10,000 British women per year - slowed the string of tumors by 40 percent, in comparison to conventional drugs. Tests conducted on 137 women showed that the new therapy, which is an injection of commonly-used Herceptin with an antibody drug, seemed to bring a temporary halt to the disease.

Those treated with the new drug lived for 14 months without the cancer becoming aggressive, compared to those who were treated with normal chemotherapy and could only spend 9 months before relapsing. The study also showed that fewer patients suffered from harmful side-effects, as opposed to those undergoing more standard treatments, reports said.

Addressing the conference at the European Multidisciplinary Cancer Congress in Stockholm, researchers said that the outcome from the trials would be used in order to examine the credibility of the drug and further decisions to consider it for further treatment options.

"This is an incredible drug. We've been looking for something like this for 20 years and this is the first of its kind. A drug like this, which increases survival chances with far less side-effects is the Holy Grail of cancer medicine," Professor Paul Ellis of Guy's Hospital told The Sunday Express.

The drug contains a protein that is designed to search for tumours and a toxin which is only discharged once inside the cancer cells, thereby reducing the chances of damage to healthy tissue. The trials were conducted at hospitals across the world, including 3 in the UK - the Christis Hospital in Manchester, the Royal Bournemouth General Hospital and the Freeman Hospital in Newcastle-upon-Tyne.

"This approach combines two effective treatments. However, until we have results from larger and longer term trials, we won't know for sure how beneficial this could be for patients with this particular type of breast cancer," Neil Barrie of Cancer Research UK, said.

Experts are currently conducting further trials on 1,000 women in over 20 countries, including Great Britain and the results are expected within two years.