In the UK, almost 46,000 new cases of breast cancer are diagnosed each year
A combination of two inexpensive existing drugs may offer a new way to treat breast cancer, according to UK and Finnish researchers.
The common chemotherapy drug and a brittle bone medicine almost completely stopped the growth of tumours in mice.
The Journal of the National Cancer Institute said the combination cost a twentieth of Herceptin, given to breast cancer patients by the NHS.
Specialists said the results of human trials now under way would be crucial.
In the UK, almost 46,000 new cases of breast cancer are diagnosed each year.
Although modern treatments mean that cases caught sufficiently early, some via breast screening programmes, have an excellent chance of being successfully treated.
The study was a joint project between researchers at the University of Sheffield and the Kuopio University in Finland.
Its findings could offer an even more effective way to help some patients.
It used a dose of the drug doxorubicin, a common component of chemotherapy regimes, followed 24 hours later by zoledronic acid, currently given to osteoporosis patients.
In the mice, this stopped 99.99% of new cancer cell growth in tumours.
It is thought the first drug could be "priming" the tumour to be more sensitive to the cancer-cell killing qualities of the second drug.
Dr Ingunn Holen, who led the study, said that the study showed that the drug cocktail could "kill breast tumours".
"These results show that a patient may benefit the most if these two drugs are given in this particular order."
She said that the results of a human trial were expected later this year.
If that proves successful, the drugs would not have to undergo a lengthy licensing process, simply have the change of use included in their current licence.
Breast Cancer Campaign, the charity which funded the study, said it was encouraged by the potential for the drug to be made swiftly available to women.
Its chief executive, Pamela Goldberg, said: "The results of this study could change the way breast cancer patients are treated.
"The good news is the that the two treatments are relatively inexpensive and already used in the clinic."
A spokesman for Cancer Research UK said that a study in humans would be important.
"Establishing the most effective combinations of drug treatments and the timings in which they are given is an important area of clinical research.
"But the benefits of giving zoledronic acid after doxorubicin have only been shown here in mice and now need to be evaluated more fully in people with breast cancer."