CHICAGO — The early success of a new class of cancer drugs, revealed in test results released here over the last several days, has raised hope among the world’s top cancer specialists that they may be on the verge of an important milestone in the fight against the disease.

The excitement has spread to Wall Street. Shares of Merck and Bristol-Myers Squibb, which are developing such drugs, rose more than 3 percent on Monday after data from their studies was presented over the weekend at the meeting of the American Society of Clinical Oncology.

The drugs, still generally in early testing, work in an entirely new way, by unleashing the immune system to attack cancer cells much as it attacks bacteria. That could be an alternative to often-debilitating chemotherapy.

Finding ways to use the body’s own defenses has been a goal since the late 1800s, when a New York surgeon named William B. Coley noticed that cancer disappeared in a patient who had a severe bacterial infection.