By Julie Steenhuysen
CHICAGO, May 15 (Reuters) - Melanoma patients treated with two Bristol-Myers Squibb drugs fared much better than those who received either of the medications individually, a new advance for treatments that harness the body's immune system to fight cancer.
Bristol released preliminary data from the early-stage trial on Wednesday, with more detailed results expected to highlight the American Society of Clinical Oncology's annual meeting in Chicago that starts at the end of the month.
Patients in the study received Bristol's immunotherapy Yervoy, which is already on the market, and an experimental treatment called Nivolumab that attacks an immune-system-inhibiting protein called PD-1. The combined treatment shrank tumors in a majority of patients.
"We have never seen this with immunotherapy before," said Dr Jedd Wolchok of New York's Memorial Sloan-Kettering Cancer Center. "The vast majority of patients have a decrease in tumor burden. In melanoma, we're used to seeing the opposite," he said of the notoriously difficult-to-treat form of skin cancer.
Investors have been eager to see results of the study, with Bristol shares reaching a 10-year high on Wednesday in advance of the data release.
Both drugs are designed to target different parts of the immune system that act as brakes even when cancer is present, preventing immune cells from attacking tumors. By gumming up these brakes, the drugs free the immune system to attack and kill tumor cells.
Approved in 2011, Yervoy, or ipilimumab, was the first drug to significantly extend survival in patients with advanced melanoma, the most deadly form of skin cancer. It boosts the immune system by blocking the action of a protein called CTLA-4.
Nivolumab, which is in late-stage testing, targets a protein called PD-1, or Programmed Death receptor, a new class of immune-system drugs that shows promise not only in melanoma but also in lung and kidney cancer.
Typically, only about 11 percent of patients respond to Yervoy, and recent studies in melanoma suggest Nivolumab produces a response rate of about 41 percent, Wolchok told a news briefing.
The current study looked at the combination of the two drugs based on animal studies suggesting that together they might work better than either drug alone.
Wolchok reported results for 86 patients in the trial as of February 2013, including 52 patients who were on both drugs at the same time. In one of the treatment groups, which will likely advance to late-stage trials, 53 percent of patients treated with both Yervoy and Nivolumab simultaneously had an objective response - defined as at least a 50 percent reduction in tumor size.
Dr Sandra Swain, president of ASCO, called the findings remarkable. "This combination treatment led to a very rapid and profound lasting tumor shrinkage. Ninety percent of patients are still responding," she said.
Three out of four patients who responded to the dual treatment had tumor shrinkage in the first three months.
Among the most advanced melanoma patients, Wolchok said the combination of the two drugs produced "rapid and deep regressions, with many showing more than 80 percent tumor regression by the time of the first scan."
Overall, most patients had some decrease in tumor size. In 31 percent of all patients taking the dual therapy, tumors shrank by greater than 80 percent, Wolchok said.
In 18 percent of patients, the drug combination produced a complete response, meaning tumors were no longer detectable, Wolchok said in an interview. He said they do not yet have any data on relapse because 90 percent of patients who responded to the treatment are continuing to benefit.
The combination also appeared to be safe. About half of patients who got both treatments had a drug-related side effect, but in most cases it was linked to elevations in enzymes related to the pancreas and liver.
"These are reversible, sometimes without treatment," Wolchok said, although some patients did need a short course of the steroid prednisone. There were no drug-related deaths.
"We really didn't see anything new with the combination" related to safety, he said.
Bristol-Myers plans a late-stage clinical trial that looks at both drugs in combination, as well as each separately, in patients with melanoma. It has also begun testing the same combination in lung cancer and renal-cell cancer.
"We view the combination of immunotherapy as a significant one that we'll be pursuing," Michael Giordano, Bristol-Myers' senior vice president of global development for oncology and immunology, said in an interview.
So far, Bristol-Myers is furthest ahead in its development of a PD-1 inhibitor, but Merck & Co Inc last month won designation from the U.S. Food and Drug Administration as a "breakthrough therapy," which could speed development and regulatory review of the product.
In a recent note, Bernstein Research analyst Tim Anderson said Bristol's anti-cancer drug PD-1 "is the major driver of investor interest at the moment," but said awareness is building that competitors "may not be very far behind."
Last November, Merck reported results from a trial of its drug in patients with advanced melanoma and saw a 47 percent response rate. In that trial, the drug benefited patients who had previously been treated with ipilimumab but had not responded, said Dr. Gary Gilliland, a Merck senior vice president for oncology.
Merck plans to present an update of this study on June 2 at the ASCO meeting. Gilliland said the company also is studying its treatment in so-called triple-negative breast cancer, a hard-to-treat form of the disease, as well as head and neck cancer and bladder cancer.
Other companies pursuing the PD-1 or related pathways include Roche, GlaxoSmithKline and Teva .
"PD-1 is arguably the most exciting breakthrough in cancer therapy in a decade," said ISI Group analyst Mark Schoenebaum. "There is speculation that it might offer a cure for some patients with solid tumors. This is unprecedented." (Additional reporting by Bill Berkrot in New York; Editing by Michele Gershberg and Prudence Crowther)