Tumour-cell genomes may hold clues to who will benefit from treatments that stimulate the immune system against melanoma.

A protein called CTLA-4 on the surface of cancer-fighting T cells can suppress these immune cells' attacks on the tumours. Drugs that block this protein can, in some patients, unleash these cells, but can have toxic side effects. Jedd Wolchok and Timothy Chan of the Memorial Sloan Kettering Cancer Center in New York and their colleagues sequenced genes in tumour cells from 64 patients with melanoma who were treated with CTLA-4 inhibitors.

Patients whose tumours had a higher number of cancer-associated mutations were more likely to benefit from the drugs, and a set of 101 tumour proteins created by these mutations were associated with a strong response to the drugs.

N. Engl. J. Med. http://doi.org/xdx (2014)