A treatment for brittle bones has a dramatic effect on breast cancer when combined with chemotherapy, research has shown.

Scientists found that the two drugs acted together to slow down the growth of tumours. In mice given the therapy, growing breast tumours were almost stopped in their tracks.

A clinical trial is now under way in the UK which could lead to the treatment becoming widely available to patients.

Since both drugs are already well established, and only need the terms of their use to be changed, this may not take long.

The therapy involves the breast cancer chemotherapy agent doxorubicin and the bisphosphonate drug zoledronic acid.

In the mouse study, doxorubicin was given first, followed 24 hours later by zoledronic acid. When the order was reversed, or the drugs administered on their own, the treatment had little effect.

The chemotherapy drug appeared to "prime" the tumour and make it sensitive to the bisphosphonate, said the scientists.

Tests showed that the treatment triggered a "suicide" response known as apoptosis in the cancer cells, causing them to self-destruct.

It also blocked angiogenesis, the process by which blood vessels are created that fuel tumours with oxygen and nutrients.

The researchers, from the University of Sheffield and Kuopio University in Finland, wrote in the Journal of the National Cancer Institute: "Tumour growth was almost completely abolished in mice treated with doxorubicin followed 24 hours later by zoledronic acid."

Bisphosphonates are normally used to prevent bone thinning in osteoporosis patients.

They have also been shown to protect the bones from the destructive effects of tumours. For this reason they are sometimes given to men with prostate cancer, which has a habit of spreading to the bones.

However the new study showed that zoledronic acid can have a powerful direct effect on breast cancer without any bone involvement. The cancer cells used had no particular affinity for bone.

Patients are now receiving the treatment in a large trial led by one of the Sheffield scientists, Professor Robert Coleman. The results should be known later this year.

Dr Ingunn Holen, from the Department of Pharmaceutics at Kuopio University, said: "Our work, using a model system, has shown that treatment with the chemotherapy agent doxorubicin followed by zoledronic acid kills breast tumours.

"These results suggest that a patient may benefit the most if these two drugs are given in this particular order."

Pamela Goldberg, chief executive of the Breast Cancer Campaign, which funded the study, said: "Despite the introduction of new treatments, every year in the UK around 12,500 people will die from breast cancer.

"The results of this study are very encouraging and could change the way breast cancer patients are treated. The good news is the two treatments used in this study are relatively inexpensive and already used in the clinic. Therefore we should quickly see the benefits of giving women the best possible chance of beating breast cancer."

Prof Coleman's trial involves 3,400 breast cancer patients. It is looking specifically at preventing the disease returning to patients.