Almost a couple of months ahead of schedule, the US Food and Drug Administration has granted accelerated approval to Merck & Co’s Keytruda for patients with advanced or unresectable melanoma who are no longer responding to other drugs.

Keytruda (pembrolizumab) is the first FDA-approved drug that blocks the PD-1 (programmed death receptor-1) cellular pathway, which restricts the body’s immune system from attacking melanoma cells. The checkpoint inhibitor is intended for use following treatment with Bristol-Myers Squibb's immunotherapy Yervoy (ipilimumab), while for melanoma patients whose tumours express the BRAF V600 gene mutation, Keytruda can be used after Yervoy and a BRAF inhibitor, like Roche’s Zelboraf (vemurafenib) and GlaxoSmithKline’s Tafinlar (dabrafenib).

24% of patients saw tumour shrink

The efficacy of Keytruda, which had breakthrough therapy status at the FDA, was established in 173 trial participants and in the half of the participants who received the drug at the recommended dose of 2mg/kg, 24% had their tumours shrink. This effect lasted at least 1.4 to 8.5 months and continued beyond this period in most patients.

An FDA decision was not expected until the end of October but approval is not surprising. Keyruda has consistently impressed in trials and is being evaluated across more than 30 types of cancers, as monotherapy and in combination - by the end of 2014, the development programme will grow to more than 24 clinical trials, enrolling some 6,000 patients.

Observers expect Bristol-Myers Squibb’s Opdivo (nivolumab) to be the next anti-PD-1 therapy to get the FDA’s blessing; last month it was approved in Japan for melanoma and will be filed in the USA by the end of the month. As for Merck, it will launch Keytruda next week, priced at $12,500 a month, or $150,000 for a year's worth of treatment.

Keytruda is the sixth new melanoma treatment approved by the FDA since 2011, the others being Yervoy, Zelboraf, Tafinlar, another Merck drug Sylatron (peginterferon alfa-2b) and GSK’s Mekinist (trametinib).