Jan. 25, 2010 (Orlando, Fla.) -- A drug combination that's been found to pack a powerful punch against the risk of colon cancer may only work in people who go light on certain foods, including red meat, corn, and orange juice, a new study suggests.
Now, the same research team has found that the drugs' dramatic polyp-lowering effect may be limited to people with a low intake of foods rich in polyamines -- chemicals in food that have been linked to an increased risk of colon cancer.
DFMO and sulindac "clearly had no benefit" in people who consume a lot of polyamines in their diet, says researcher Kavitha Raj, MD, of the University of California, Irvine.
The Role of Polyamines
For the new study, Raj and colleagues went back and reanalyzed data on about 200 people who participated in their original study of DFMO and sulindac. All had at least one colorectal polyp, also known as adenomas, removed in the past year.
Participants were divided into four groups depending on their level of polyamine intake.
First, the researchers analyzed tissue samples that had been taken from the participants before they started the study. They found that compared with those with the lowest intake, people with the highest consumption of polyamines had larger polyps and more advanced polyps with a greater odds of going on to cancer.
Then the researchers looked at the impact of polyamine levels on the study results. In the study, patients were assigned to treatment with either a combination of DFMO and sulindac, or placebo.
In the original study, in which participants were not stratified by polyamine intake, colonoscopy exams after three years showed that people who took DFMO and sulindac were 70% less likely to develop a new polyp, compared with people given a placebo.
The picture drastically changed when polyamines were taken into account, Raj says.
People in the lowest quartile of polyamine intake were 81% less likely to have developed a new polyp than people given a placebo. They were also 89% less likely to have large adenomas and 94% less likely to have advanced adenomas.
"In people in the highest quartile of polyamine intake, however, DFMO and sulindac had no benefit whatsoever," Raj says.
"Too much polyamine is decreasing the effect of the drug seen in the original study," she says.
The findings help to refine who will most benefit from this colon cancer preventive strategy, says Richard M. Goldberg, MD, head of the North Carolina Cancer Hospital in Chapel Hill.
"Prevention studies are probably the answer to cancer," he tells WebMD. "That's how we will make the biggest impact on [deaths]." Goldberg was not involved in the study.
When it comes to polyamines, it's still not known how much is too much, Raj says. "But people in the highest quartile in the study are eating about 50% more [than the average person]," she says.
Foods rich in polyamines include orange juice, red meat, corn, and peas.
DFMO, which is short for difluoromethylornithine, was developed as a cancer medication but is now used to treat African sleeping sickness. It's also used to remove unwanted hair. Sulindac, a nonsteroidal anti-inflammatory drug (NSAID), is also sold as Clinoril.