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Scientists have designed a special type of drug that helps the body eat and destroy cancerous cells.

The treatment boosts the action of white blood cells, called macrophages, that the immune system uses to gobble up unwanted invaders.

Tests in mice showed the therapy worked for aggressive breast and skin tumours, Nature Biomedical Engineering journal reports.

The US team behind the study hope to begin human trials within a few years.

The drug that they designed already has a licence, which they say should hasten the approval process.

It is a "supramolecule" - a drug built from component molecules that fit together like building blocks.

Treatments that target the immune system to fight cancer are a growing area of research that lots of scientists around the world are investigating.

This latest work involves a devouring or "phagocytic" immune cell called the macrophage.

Eating cancer

Macrophages are already good at fighting bacterial and viral infections because they can recognise and attack these "foreign" invaders.

But they are not so effective at tackling cancer, since tumours grow from our own cells and have clever mechanisms to hide from immune attack.

The drug Dr Ashish Kulkarni and colleagues at Harvard Medical School's Brigham and Women's Hospital used in their study works in two ways.

Firstly, it stops cancer cells from hiding and sending out "eat me not" signals to macrophages. Secondly, it prevents the tumour from telling macrophages to turn docile.

The supramolecular therapy appeared to stop cancer from growing and spreading in the test mice.

The researchers envisage that it could be used alongside other cancer treatments such as checkpoint inhibitors.

Carl Alexander, from Cancer Research UK, said: "It's promising to see yet another new approach. More work is now needed to show that this approach could be used to treat cancer patients."