SAN FRANCISCO (AP) - 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.''

Dr. Edwardo deMoraes of Thomas Jefferson University reported on testing of angiostatin on 19 patients with advanced colon, breast, ovarian and head and neck cancer. Their tumors did not shrink, although in three the cancer stopped growing for six months.

Dr. Kathy Miller of Indiana University said 24 women with advanced breast cancer have taken Panzem, which is derived from estrogen, the female hormone. Some had extremely fast growing cancer, which in a few cases has slowed or stopped, even though it has not gone away.

``This has been very encouraging,'' said Miller. ``Stable disease with a nontoxic therapy is a good deal.''

Dr. Roy Herbst tested endostatin at M.D. Anderson Cancer Center in Houston, as did researchers at the University of Wisconsin and the Dana-Farber Cancer Center in Boston. At each center, doctors saw one or two patients who seemed to be helped by the drug temporarily, even though their cancers eventually continued to grow.

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.

Among other reports at the meeting:

-Gleevec, a drug approved last week for a rare form of leukemia, also shows promise against an unusual digestive cancer called gastrointestinal stromal tumors, or GIST. In a study of 148 patients, half of the patients went into remission, and 90 percent benefited at least somewhat. The drug is also being tested in lung, prostate and brain cancer.

-In a small study at Stanford University, researchers found it may be possible to treat advanced colon cancer with a vaccine made from patients' own cells. They altered cells called dendritic cells so they carry a protein found on cancer cells. Injected back into the body, they triggered a powerful immune system attack on the cancer.

Copyright 2001 The Associated Press. All rights reserved.