ORLANDO, Fla. -- An experimental, targeted cancer drug from

Abgenix

(ABGX)

appears to be effective in helping some patients with advanced kidney cancer, one of the most stubborn, difficult-to-treat cancers out there.

The Fremont, Calif.-based biotech firm reported positive findings on Tuesday from a phase II clinical trial of the drug, known as ABX-EGF, at the meeting of the American Society of Clinical Oncology. ABX-EGF is among a closely watched class of drugs that attempts to halt the growth of cancer cells by blocking a key enzyme, epidermal growth factor receptor.

ImClone Systems

(IMCL)

,

AstraZeneca

(AZN) - Get Report

,

Genentech

(DNA)

and

OSI Pharmaceuticals

(OSIP)

are all working on similar new drugs.

These so-called EGF inhibitors are being tested against a wide variety of cancers, but so far only ABX-EGF has shown significant results in treating kidney cancer. A small study testing AstraZeneca's Iressa on patients with advanced kidney cancer, reported at the ASCO meeting on Sunday, yielded no positive results. ImClone's drug, Erbitux, hasn't had much luck against the cancer either.

There hasn't been a new drug developed for kidney cancer in about 10 years. What has Abgenix researchers excited about Tuesday's findings is that ABX-EGF shows evidence of working in some patients who have failed all current treatment options.

Abgenix is co-developing ABX-EGF with the biotech firm

Immunex

(IMNX)

, which is in the midst of a merger with

Amgen

(AMGN) - Get Report

.

Researchers reported Tuesday that five of 88 patients with advanced kidney cancer responded to ABX-EGF, or 6% of patients in the study. That means their tumors partially shrank. These patients, on average, had already tried and failed three prior drug therapies. In another 44, or 50%, of patients, their tumors stopped growing.

The 88 patients in the study were divided into four groups, each of which received a different dose of ABX-EGF. The low and high doses of the drug worked best, although Abgenix, in previous studies, has determined that the high dose appears the most promising.

"These preliminary, phase II results are very encouraging and suggest that ABX-EGF is a promising, single agent therapeutic approach to solid tumors," said Dr. Eric Rowinsky of the University of Texas, one of the study's authors.

Dr. Gisela Schwab, Abgenix's chief medical officer, says Tuesday's positive results provide the basis for further study of ABX-EGF in kidney cancer. While it may be too early to tell exactly why ABX-EGF is succeeding where rivals have failed, Schwab postulates that her company's drug may be a more potent inhibitor of the epidermal growth factor receptor.

An acnelike skin rash is the most common side effect of EGFR inhibitors, but it's also a signal that the drug is saturating the body and reaching tumors. When given at its highest dose, ABX-EGF causes skin rash in 100% of patients. This doesn't mean, however, that EGFR inhibitors must cause skin rashes in all patients to prove effective.

Moving forward, Abgenix and Immunex -- soon to be Amgen -- are conducting four other phase II studies of ABX-EGF against colorectal, lung and prostate cancer. The drug is being tested both as a monotherapy and in combination with existing chemotherapy drugs. Results from one of two colorectal studies will be released by the end of the year.

Abgenix is trading down 66 cents, or 4.5%, to $13.84.