Many solid tumours, including many cancers of the pancreas, breast, colon and lung, protect themselves with a dense wall of scar-like tissue. That wall keeps the immune system’s cancer killing T cells out.

It is a major reason why immunotherapy drugs, which have transformed treatment for some patients, help only a minority of people with solid tumours.

A study published today in Cancer Cell describes an experimental drug that breaks down this barrier from inside the tumour and lets T cells in to attack.