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SAN FRANCISCO — Much-anticipated new drugs intended to stop cancer by cutting off its blood supply show only slight benefit in early testing on terminally ill patients, although experts say the medicines still may prove useful. 

Whatever their eventual role, however, new data released Sunday suggest the drugs will not be the kind of across-the-board cancer cure that some had predicted. 

None of the drugs prompted the kind of dramatic tumor shrinkage or disappearance that doctors look for even in the first stages of human testing, which are largely intended to see if medicines are safe. Although the drugs had little effect overall, there were hints they might sometimes slow or even stop some tumor growth, at least temporarily. 

Reports on three of the drugs, all discovered in the lab of Dr. Judah Folkman, were presented at a meeting in San Francisco of the American Society for Clinical Oncology. 

Folkman, a surgeon at Boston’s Children’s Hospital, pioneered the field called angiogenesis, which involves trying to starve tumors with chemicals that stop them from building new blood vessels. 

Many angiogenesis drugs are being tested, but the two highest-profile candidates are endostatin and angiostatin, discovered in Folkman’s lab by Dr. Michael O’Reilly. A frenzy erupted over them in 1998 when an optimistically worded article in The New York Times quoted scientists predicting the drugs would soon provide a cancer cure. 

The latest data suggest this is unlikely. Doctors updated preliminary findings on endostatin research that were first released in November. Sunday’s presentations were the first on human testing of angiostatin and Panzem, another blood vessel blocker discovered by Folkman’s team. 

“The data are encouraging but not yet definitive,” O’Reilly said. “There is enough information to suggest that angiogenesis inhibitors will be used in the clinic. It’s just a question of which ones.” 

Doctors said that in some patients, the drug seems to halt cancer in some parts of the body while having little effect elsewhere. Overall, however, scans shows that the flow of blood to the patients’ tumors decreases. 

The next step will be to test these drugs in people with less advanced disease and to combine them with chemotherapy and radiation, as well as perhaps other medicines that block blood vessel growth. Some speculate that long-term use will hold cancer in check without curing it. 

Dr. Larry Norton of Memorial Sloan-Kettering Center said many have wondered whether it will do any good to cut off new blood vessels to tumors that already have a blood supply. 

“In many ways, it was miraculous that there was any biological effect at all,” he said.