Amgen says test does not flag panitumumab response
LOS ANGELES (Reuters) – Amgen Inc. said on Saturday that
testing tumors for the protein that its experimental colon
cancer drug panitumumab is designed to target is not an
accurate measure of whether a patient will respond to the
Two clinical trials funded by Amgen show that some patients
who tested negative for epidermal growth factor receptor, the
protein on the surface of cancer cells that the drug is
designed to block, responded to the treatment, while others who
tested positive did not see an improvement.
“This should put the final nail in the coffin of this
test,” said Dr. J. Randolph Hecht, director of the UCLA
gastrointestinal oncology program and lead investigator of one
of the studies.
He explained that many insurance companies will only pay
for a similar drug, ImClone Inc.’s Erbitux, if patients have a
positive “EGFr stain” test.
“It adds another layer of complexity for these patients who
don’t need it,” Hecht said.
Amgen said its findings came from two mid-stage trials
involving patients with advanced colon cancer who did not
respond to standard chemotherapy.
The first study examined patients with tumor EGFr levels of
less than 1 percent, while the second evaluated patients with
levels of at least 10 percent.
Preliminary results for the first study included 23
patients. Thirteen percent who received panitumumab had a
partial response, including two patients with tumor cells
negative for EGFr, and stable disease was observed in 30
percent of patients.
The study of patients with higher EGFr levels had 39
available for evaluation. After 16 weeks, 8 percent showed a
partial response, 21 percent had stable disease and 49 percent
had their cancer get worse.
The most common side effects seen in the trials were skin
irritation, fatigue, abdominal pain, nausea and diarrhea.
Amgen expects a U.S. Food and Drug Administration decision
on whether to approve panitumumab for advanced colon cancer in
the second half of this year.
Hecht said several groups of researchers are working to
develop alternate tests that would determine which patients are
the best candidates for the drug.
The study results were presented in Atlanta at a meeting of
the American Society of Clinical Oncology.