Scientists have successfully blocked the spread of human breast cancer implanted into mice.
Cancer cells are sticky
If breast cancer - and other forms of the disease - can be stopped from spreading around the body, then many lives could be saved.
A team from the San Francisco VA Medical Center were able to stop the cancer in its tracks by using a modified version of a naturally occurring human protein.
The treatment appeared to be side effect free.
It works by reducing the "stickiness" of cancer cells. It is the ability to adhere to other cells that allows a cancer cell that breaks away from a primary tumour to lodge in other parts of the body, and trigger the growth of new malignancies.
What we're trying to do is make cancer a disease that one can live with
Researcher Dr Constance John said: "We're not trying to develop a cure for cancer.
"What we're trying to do is make cancer a disease that one can live with."
The new technique involves the modification of a human protein called galectin-3, which plays a crucial role in making cancer cell sticky.
The researchers effectively robbed the protein of this ability by changing its structure.
They then implanted portions of human-derived breast cancer tumours into mice with weakened immune systems.
Once the tumours were established, some mice were injected with the modified protein, and others were given a dummy treatment.
By the end of the experiment, cancer had spread to lymph nodes or other organs in 11 of the 20 mice given the dummy injection - but only four of the 20 who received the modified protein.
In addition, the original implanted cancer fragments had grown significantly less in the "treated" mice.
The researchers hope that a drug therapy based on their findings may one day be used in combination with currently available cancer medications.
Lead researcher Dr Gary Jarvis said: "If we can stop metastasis (spread) in humans, we will have gone a long way towards successfully treating cancer."
Martin Ledwick, senior cancer information nurse for the charity CancerBACUP, said: "These experiments are interesting, but people should not get over-excited.
"It will be a long time before we know whether this study is at all relevant for the treatment of cancer in humans."
Anna Wood, a policy analyst for the charity Breast Cancer Care, echoed this opinion.
She said: "This treatment has only been tested on mice and we would advice caution when interpreting the results."
The research is published in the journal Clinical Cancer Research.