A pill that “wakes up” the immune system allowing it to kill spreading tumours could one day bring new hope to people with advanced cancer.

In tests on mice, scientists used a drug to activate natural killer (NK) cells, part of the innate immune system and the body’s first line of cancer defence.

A major problem with progressing cancer is that it develops ways to “turn off” NK cells so that they no longer recognise their enemy.

As a result cancer is permitted to spread around the body unchecked. The spread of disease to vital organs, or metastasis, is the chief cause of death in cancer patients.

The new molecule, known as a TAM kinase inhibitor, effectively removes the brakes from natural killer cells so they can destroy metastatic cancer.

Mice with spreading cancer responded well when given the treatment, either through injection or by mouth, and displayed no serious side effects.

Reporting their findings in the journal Nature, the scientists led by Josef Penninger, from the Austrian Academy of Sciences in Vienna, wrote: “This novel... pathway shows that it might be possible to develop a ‘pill’ that awakens the innate immune system to kill cancer metastases.”

The blood-thinning drug warfarin, which targets the same TAM pathway, was also shown to combat metastasis in mice.

This finding could explain the long-standing puzzle of why cancer patients treated with warfarin sometimes show signs of improvement.