Pfizer drug slows pancreatic cancer
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NEW YORK -- An experimental drug made by Pfizer Inc. slowed deadly pancreatic cancer in a study that revealed a new treatment approach that tricks the immune system to attack tissue protecting tumors, researchers say.
Four of 21 patients with incurable pancreatic cancer had their tumors shrink after being given the drug, known as CP- 870,893, along with Eli Lilly's Gemzar chemotherapy, according to the study published Thursday in the journal Science. The median time before the disease progressed was 5.6 months compared with 2.3 months expected for patients taking just chemotherapy, researchers said. More surprising, biopsied tissue samples showed the treatment didn't do what scientists expected.
Designed to activate immune system T-cells to attack the tumor, tests revealed the Pfizer drug instead spurred an abundance of white blood cells, called macrophages. Those cells, which normally protect tumors, had been retrained to attack the cellular structures supporting the cancer, the scientists said.
"Until now, we thought the immune system needed to attack the cancer directly in order to be effective," said lead author Robert Vonderheide, a cancer professor at the University of Pennsylvania's Abramson Cancer Center. "We think that this may be a general approach for treating other types of solid tumors."
In addition to the four patients who had their tumors shrink, 11 patients had their disease stabilize. The cancer eventually progressed for all of the patients in the study.
Now that researchers understand how the drug worked, they are working on ways to boost the macrophage response, Dr. Vonderheide said. The trial was in the first round of human tests typically used to evaluate safety and dosing.
Pfizer, the world's biggest drugmaker, is currently conducting two early tests using the drug to treat melanoma, said Dr. Vonderheide, who is working on one of the studies, which combines the treatment with another experimental Pfizer antibody.
The medicine still requires larger successful tests, which typically take years to conduct, before the New York-based company might seek regulatory approval.
Pancreatic cancer kills about 37,000 people in the United States each year, according to estimates by the National Cancer Institute in Bethesda, Md. Just 4 percent of patients are still alive five years after being diagnosed with pancreatic cancer, according to the American Cancer Society, based in Atlanta.
The report published Thursday includes clinical trial results and laboratory results in mice. It is an example of a new model of research that speeds discoveries by taking results in humans back to the lab to conduct tests in genetically engineered mice. The study team was made up of laboratory scientists and clinical doctors, Dr. Vonderheide said.
First Published March 26, 2011 12:00 am