Time to rethink colon cancer therapy?

CHICAGO (Reuters) - Adding the drug cetuximab (Erbitux) to standard treatments does not help patients with early stage colon cancer even though it does help patients with advanced disease, a perplexing finding that is causing doctors to question some basic assumptions about cancer drugs, they said on Sunday.

The study of the Eli Lilly and Bristol-Myers biotechnology drug cetuximab was stopped early because it failed to show a benefit in early stage colon cancer patients when added to standard treatment.

"This trial is important," said Dr. Steven Alberts of the Mayo Clinic College of Medicine in Rochester, Minnesota, who presented the results at the American Society of Clinical Oncology meeting in Chicago. It indicates that disease in early stage may be different than in later stage, he said in a media briefing. "Clearly, it is important to understand why the drug did not work," he added.

The cetuximab study follows the failure last year of bevacizumab (Avastin) in early stage colon cancer. Both drugs are approved for sale in patients with advanced disease.

Cetuximab is a monoclonal antibody that works by blocking epidermal growth factor receptor (EGFR), a gene that is overactive in many types of cancer cells.

Bevacizumab interferes with the blood supply to the tumor.

Both drugs are in the so-called biologics class, but cetuximab works only in the 60 to 65% of patients whose tumors contain the normal version of the KRAS gene, a common gene that sends growth signals from EGFR to the cancer.

Doctors have long assumed that if a drug works in patients with advanced disease, it should work in patients with early stage disease as well.

In the cetuximab study, doctors tested patients to ensure they had the normal version of the KRAS gene. Even so, the treatment did nothing to extend survival.

"It casts doubt on whether biologics will play a role in early stage colon cancer," said Dr. Jennifer Obel of Northshore University Health System in Illinois, moderator of a media briefing at the meeting.

"It makes us want to think if that disease state is unique," Dr. Obel said.

Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society, said the two studies defy conventional thinking about cancer drugs.

"Erbitux and Avastin both failed in early stage trials. Logically, you would think they would have been a home run."

"Maybe we have to rethink how we think about what we look for in some of these newer treatments," Dr. Lichtenfeld said.