Frankfurt, German ? A new drug designed to stop cancer by cutting off its blood supply has surprised experts by showing a tumor shrinkage rate unprecedented for a drug so early in its development.

In the first human trials, involving 23 people with terminal cancer, the tumors of one-quarter of the patients shrank by half or more.

The drug, which does not yet have a name, is a newcomer to the field of anti-angiogenics ” drugs designed to damage tumors by attacking blood vessels that feed them.

Although it has been a major focus of research over the last decade, anti-angiogenesis has not lived up to its early research promise.

Experts said they believe part of the reason the new drug seems so much more powerful than others of its class is that it attacks from three directions instead of just one.

As well as blocking a protein involved in blood vessel growth called vascular endothelial growth factor, the new drug also interferes with two other blood vessel growth factors ” basic fibroblast growth factor and platelet-derived growth factor. Some scientists suspect those enzymes might do more than just support blood vessel growth.