In a separate early stage study, nivolumab on its own was shown to extend survival to one year in 43 percent of patients with non-small cell lung cancer, 61 percent of patients with melanoma and 70 percent of kidney cancer patients.
Roche released preliminary data which showed its drug resulted in meaningful tumor shrinkage in more than 20 percent of patients with advanced lung cancer, melanoma, kidney, and other cancers. As a result the drug maker is moving to a late stage trial with lung cancer patients.
Preliminary data show Merck's experimental immunotherapy drug lambrolizumab reduced tumors by 38 percent in patients with advanced melanoma. Last month, the Food and Drug Administration designated the drug as a Breakthrough Therapy.
(Read More: Investors Pour Big Money Into US Biotech)
The promise of these drugs to treat a wide variety of cancers has many investors seeing potential new blockbusters for the pharmaceutical industry, said veteran pharmaceutical analyst Barbara Ryan, who is now a managing director at FTI Consulting.
"The expectation financially is that these are going to revolutionize treatment, they can be added on to other therapies and could be five to 10 billion dollars" in annual sales, she said.
So far, investors have placed big bets on Bristol-Myers to be a leader in the new treatment category. The company's stock has gained more than 40 percent in 2013, in part on the promise of its combination treatment, and also because of the already dominant market share for Yervoy in melanoma treatment.
But ISI Group's Mark Schoenebaum says Merck, which has been one of the laggards this year in the Dow Jones Industrial average, could see a bounce from its news at ASCO. The company has scheduled an analyst meeting at the event.
"I'm going to be very interested in the meeting to find out whether or not Merck can do anything to catch up with Bristol Meyers," Schoenebaum said.
Barbara Ryan notes more companies than usual are hosting meetings at this year's conference, "which is a demonstration of the fact that they think they have a lot of good news to share."
New Cancer Entrants
New cancer trial data from companies better known for producing specialty drugs is another trend to watch at ASCO.
Gilead Sciences, better known for producing leading treatments in HIV and now Hepatitis C, will present phase II stage data on idelalisab, a drug to treat advanced chronic lymphocytic leukemia. Its study abstract released earlier this month showed patients experienced a 56 percent rate of tumor shrinkage.
The blood cancer treatment marks Gilead's first foray into oncology, but it's not the only one making a debut in cancer care.
Biomarin, a drug maker that specializes in drugs to treat rare diseases, will present early trial results on a drug to treat breast and ovarian cancer in patients with specific genetic markers. Biomarin's chief medical officer, Hank Fuchs, said a precisely targeted approach was key to the development of the experimental drug.
(Read More: Merck in $5Billion Buyback Deal With Goldman Sachs)
"The therapy that we designed does exactly what we designed it to do. It doesn't do a lot of other stuff," he said. "It hurts the tumor."
As a result, patients tolerated the treatments much better than traditional chemotherapy, he said, "because it's so selective to what the tumor's problem is, they don't have a lot of side effects."
Barbara Ryan said that's a major step forward cancer for treatments.
"The hope is that these drugs allow people to be more productive," said Barbara Ryan. "Many of these new therapies could help transform cancer care, much the way anti-viral drugs have helped AIDS patients manage their disease."
—By CNBC's Bertha Coombs. Follow her on Twitter
(CORRECTION: An earlier version of this story incorrectly said that lambrolizumab reduced tumors by 35 percent, but Merck's most recently released data showed a 38-percent reduction.)