Merck & Co. (MRK), Bristol-Myers Squibb Co. (BMY) and Roche Holding AG (ROG) have opened a new front against cancer with the next generation of experimental drugs that use the human immune system to seek and destroy tumor cells.

The new therapies have the potential to reap billions of dollars in sales while lengthening patient remissions, said doctors and analysts awaiting study results to be released this week as part of the American Society of Clinical Oncology meeting that starts May 31.