There is currently little evidence for the efficacy of vaccines to limit the progression of metastatic cancer. Vaccine treatment (sipuleucel-T) has been associated with increased survival in men with prostate cancer (N Engl J Med. 2010;363:411-422), but a recent high-quality trial investigating the GP100 vaccine in patients with metastatic melanoma found no survival benefit for the combination of vaccine plus ipilimumab compared with ipilimumab alone and found reduced survival in patients receiving vaccine alone (N Engl J Med. 2010;363:711-723).
However, a new trial indicates that GP100 plus interleukin-2 increases clinical response, delays recurrence and may improve survival (N Engl J Med. 2011;364:2119-2127).
A total of 185 patients with stage III-IV melanoma without brain metastases were randomized to GP100 plus incomplete Freund’s adjuvant in combination with interleukin-2 vs. interleukin-2 only. The GP100 group received the vaccine once per three-week cycle. All patients had interleukin-2 at a dose of 720,000 units/kg IV bolus every eight hours up to 12 doses per cycle. Complete clinical response was defined as disappearance of all lesions.
At mean follow-up of 41.5 months, the GP100 group had significantly higher rates of both complete clinical response (9% vs. 1%; P=0.01; NNT=13) and any clinical response (16% vs. 6%; P=0.03; NNT=10), and had longer progression-free survival (median 2.2 months vs. 1.6 months; P=0.008). Also, there was a trend toward increased overall survival in the GP100 group (median 17.8 months vs. 11.1 months, P=0.06). The risk of arrhythmias was significantly increased in the GP100 group (15% vs. 2%; P<0.002; NNH=7).