Experimental therapies that unleash the immune system to fight cancer, by blocking 'checkpoint inhibitors', continue to show promise in early clinical trials.

Immune checkpoint inhibitors prevent autoimmunity, and can rein in the immune response against tumours. Antoni Ribas at the University of California, Los Angeles, and his colleagues tested lambrolizumab, a compound that blocks a checkpoint inhibitor called PD-1, in 135 people with advanced melanoma. Tumours shrank by at least 30% in 38% of the patients.

In a separate study, Jedd Wolchok at Memorial Sloan-Kettering Cancer Center in New York and his colleagues, treated 86 people with advanced melanoma using two compounds: nivolumab, also a PD-1 inhibitor, and ipilimumab, an approved drug that blocks a checkpoint inhibitor called CTLA-4. Tumours shrank by at least half in 40% of the patients.

N. Engl. J. Med. http://dx.doi.org/10.1056/NEJMoa1305133; http://dx.doi.org/10.1056/NEJMoa1302369 (2013)