April 3, 2006 (Washington) -- Salad anyone? A new study in rats suggests that well-done beef, chicken, and even fish contain a substance that may promote the growth of prostate tumors.
Switching preparation methods may not help: Grilling, searing, and broiling are all equally risky, says researcher Angelo DeMarzo, MD, of the Johns Hopkins Kimmel Cancer Center in Baltimore.
The researchers studied a chemical called PhIP that is formed by cooking so-called muscle meats such as beef, pork, fowl, and fish at very high temperatures. The process sets off a chemical reaction between a protein and a chemical found in the meat, and the two come together to form a new substance that is a suspect in cancer.
According to DeMarzo, the substance was discovered by a Japanese chemist who was watching his wife cook fish. "It occurred to him that the smoke coming off the grill may have carcinogenic [cancer-causing] chemicals," he says.
Sure enough, early studies showed that rats fed PhIP developed precancerous lesions of the prostate -- but only in the front, or ventral, part of the organ.
PhIP a Double Whammy
To begin to unravel why the lesions congregate in this area, DeMarzo's colleague Yasutomo Nakai, MD, started mixing PhIP into rats' meals. Their findings were presented at the annual meeting of the American Association for Cancer Research.
After just four weeks, the rats had significantly more mutations in their prostates than rats not slipped the chemical.
But mutations alone don't cause cancer. First they have to be initiated, a process in which the mutated cells divide and divide and divide some more, producing more and more copies of themselves that carry the mutation.
And in the rats fed PhIP, there was a significant rise in the number of cells undergoing division only in the front part of the prostate, "which suggest strongly that the chemical is acting as an initiator in the ventral area alone," DeMarzo says.
But even initiated cells, left alone, are relatively harmless. They can only become tumor cells if acted upon by a promoter -- substances that cause these cells to replicate and grow more quickly. And after eight weeks on the PhIP-rich diet, there was a significant increase in proliferation only in the front part of the prostate.
"In other words, this chemical acts as both an initiator and a promoter of cancer cells, but only in the frontal lobe. It's a double whammy," DeMarzo tells WebMD.
Inflammation May Drive Process
But the researchers still didn't know why the frontal part of the prostate was so attractive to the cancer-causing process. And then they observed an increase in certain inflammatory cells in the same region.
Since inflammation is known to cause cancer in many organs, these cells may be driving the process, DeMarzo says.
"Now we have to take it to the next step and see if the inflammatory cells are innocent bystanders or really are playing a role in causing the disease," he says.
A Warning for Men With Early Cancer
Christine B. Ambrosone, PhD, of the division of cancer prevention and population sciences at the Roswell Cancer Institute in Buffalo, N.Y., says the findings may have important implications for men with early prostate cancer.
Many prostate cancers are so slow growing that doctors may recommend a strategy of watchful waiting to see if the cancers will actually cause problems before starting treatment.
"But this suggests that [cooking meat at very high temperatures] may make these early tumors grow more quickly," Ambrosone tells WebMD. "Even while we await confirmation in humans, it's not like avoiding well-done meat will do any harm."