Merck & Co and Bristol-Myers Squibb (BMS) both presented positive phase III data for their anti-PD-1 melanoma candidates at the American Society of Clinical Oncology (ASCO) conference in Chicago, US, over the weekend as optimism builds for the new drug class.
Merck presented data from a phase II study - simultaneously published in the New England Journal of Medicine (NEJM) - which showed that its antibody-based drug lambrolizumab (formerly MK-3475) achieved a response rate of 38 per cent in advanced melanoma patients.
The response rate was as high as 52 per cent among patients on the highest dose tested, and seemed to occur regardless of whether they had been treated previously with BMS' CTLA-4 inhibitor Yervoy (ipilimumab) therapy, which is fast becoming the first-line treatment of choice for advanced melanoma.
"The overall median progression-free survival among the 135 patients was longer than 7 months," said the researchers, a result which compares favourably with typical PFS expectations in patients with advanced melanoma.
Merck said it intends to move directly to phase III trials later this year for the drug, which was awarded breakthrough status by the FDA in April.
Lambrolizumab is an antibody against the programmed death-1 (PD-1) receptor, in the same class as BMS' phase III candidate nivolumab, which was also the subject of new data presentations at ASCO, as well as Roche's MPDL320A.
The drugs all work by prompting the patient's own immune system to mount a T cell-mediated immune response against melanoma by stripping away a mask adopted by the tumour cells to help them evade detection.
The NEJM published another study (also presented at ASCO) in which nivolumab was combined with Yervoy to achieve "rapid and deep tumour regression in a substantial proportion of patients," according to the researchers.
The 53-patient study revealed that 53 per cent of patients at the highest tolerable dose of the combination achieved an objective response with tumour reductions of 80 per cent or more.
Meanwhile, a phase I study presented at ASCO revealed response rates of 31 to 41 per cent for nivolumab among patients with hard-to-treat stage 4 melanoma, compared to typical responses of just 5 to 10 per cent with Yervoy in this heavily-pre-treated population.
And unlike CTLA-4 inhibitors that sometimes take several months to induce a response, 45 per cent of patients who responded to nivolumab showed at least 30 per cent tumour shrinkage just eight weeks after starting treatment.
BMS is conducting three phase III trials of nivolumab in melanoma, plus additional late-stage trials in lung and kidney cancer, and the drug has been predicted to make sales of $1.2bn a year at peak. As it is likely to be second to market behind nivolumab, lambrolizumab has lower sales projections, with some analysts predicting turnover of $500m-plus a year.