An experimental drug from Amgen Inc. and Abgenix Inc. reduced tumors in about 9 percent of patients with advanced Colon cancer who previously failed to benefit from chemotherapy, according to independently confirmed trial data presented on Tuesday.

Patients in the mid-stage trial survived for a median 37.6 weeks, according to researchers at Loma Linda University Cancer Institute in Loma Linda, California.

The analysis confirms previously reported results from the 148-patient trial of the drug, called panitumumab, a monoclonal antibody that works by blocking a protein called epidermal growth factor that helps tumors grow.

The results are close to those seen for patients taking Erbitux, a similar antibody sold by ImClone Systems Inc. and Bristol-Myers Squibb Co., said Dr. David Parkinson, head of Amgen’s oncology therapeutic area.

But the fact that panitumumab is a “fully-humanized” antibody that can be given less frequently than Erbitux, which contains fragments of mouse proteins, could be an advantage, Parkinson said.

A separate trial, also presented here at a meeting of the American Society of Clinical Oncology, showed that the drug’s safety was the same when given weekly, every other week and every three weeks.

“If we didn’t think this was a potentially more potent antibody, we wouldn’t be doing this,” Parkinson said.

The most common side effect of panitumumab was a reversible skin rash.

The drug, which is given intravenously, would also face competition from synthetically made “small-molecule” drugs, such as Tarceva, sold by Genentech Inc. and OSI Pharmaceuticals, and AstraZeneca’s Iressa, that are also designed to target the EGFR receptor.

Parkinson said there appear to be differences between antibodies and small molecules in terms of biological impact and researchers are beginning to understand which patients will benefit the most from which drugs.

Amgen will have results from a late-stage Colon cancer trial of panitumumab late this year or early next year and expects regulatory approval in 2006, he said.

If approved, panitumumab would be the first actual cancer drug for Amgen, which has sales in the billions for products that treat anemia and other side affects of chemotherapy.