Preliminary results of two international trials on experimental treatments for advanced stage skin cancer were presented this week at the American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago. Two experimental drugs, pembrolizumab and nivolumab, target the means by which cancer cells remain hidden from the body’s immune system

If it detects them, the immune system destroys cancer cells, but cancer cells typically go undetected because they “hide” from the immune system’s surveillance system. In one trial of 411 patients on pembrolizumab (previously known as MK-3475) with advanced melanoma, an aggressive and stubborn form of skin cancer that has spread to other organs of the body, 69 percent survived at least one year. For years the average survival for advanced melanoma was only about six months.

Pembrolizumab is also being looked at in the treatment of other forms of cancer.

“Pembrolizumab looks like it has potential to be a paradigm shift for cancer therapy,” said Dr. David Chao of the Royal Free London NHS Foundation Trust and scientist on the trial. Chao has another ongoing trial of the drug in treatment for lung cancer.

The other trial involves the combination of Nivolumab with ipilimumab, licensed immunotherapy drug already used in cancer treatment. Among 53 melanoma patients in the trial, 85 percent survived one year, and 79 percent survived an additional year for a total of two years of life after diagnosis with metastatic melanoma.

“I am convinced that this is a breakthrough in treating melanoma,” said John Wagstaff of Swansea College of Medicine in the UK. “The trial is still ‘blinded’ so we don’t know what treatments the patients are getting, but we have seen some spectacular responses.”

The results for both trials represent Phase I findings. Larger Phase II and III studies are necessary before these results can be interpreted with confidence.

Both pembrolizumab and novolumab are monoclonal antibodies that were generated against specific protein targets found on cancer cells. Pembrolizumab was developed by Merck to attack the programmed cell death-1 (PD-1) receptor. Nivolumab was developed by Bristol-Myers Squibb (BMS) and blocks ligand activation of PD-1 receptor. The approved drug Ipilimumab is also BMS-developed monoclonal antibody that inhibits the CTLA-4 receptor that normally attenuates immune system activity.

The 2014 ASCO Annual Meeting abstracts are available online to the public.