WEDNESDAY, Aug. 6, 2008 (HealthDay News) -- Vietnam veterans exposed to the defoliant Agent Orange have a significantly greater risk of prostate cancer, especially the most aggressive form of the disease, a new study contends.
The findings are the first to connect the now-banned herbicide with this form of cancer, the researchers said.
"Veterans that were exposed to Agent Orange during the Vietnam War have a twofold higher risk of prostate cancer," said study lead author Dr. Karim Chamie, a resident physician in urology at the University of California, Davis, Department of Urology and the VA Northern California Health Care System. "The cancer they get tends to be more aggressive, a higher grade, and is more likely to spread or have spread at the time that they present to their urologist."
"A lot of veterans don't get their care through the VA [Veterans Administration]," Chamie added. "This message needs to go out to their physicians and their urologist in the private community to know that this is a large risk factor."
But some scientists not involved with the study said the research does not prove a cause-and-effect relationship between Agent Orange and prostate cancer.
For the study, Chamie's team collected data on 13,144 Vietnam veterans, including 6,214 men exposed to Agent Orange between 1962 and 1971.
The researchers found that twice as many veterans exposed to Agent Orange had developed prostate cancer, compared with veterans not exposed to the now-banned chemical.
Moreover, men exposed to Agent Orange were diagnosed with prostate cancer two-and-a-half years younger than unexposed men. And, they were four times more likely to be diagnosed with metastatic disease, the researchers found.
The findings were published online Monday in Cancer and were expected to be published in the Sept. 15 print issue of the journal.
Agent Orange is made up of compounds known to be contaminated with the dioxin tetrachlorodibenzo-para-dioxin (TCDD) during manufacture. The chemical was named for the color of the barrel it was stored in and was one of the "broad-leaf defoliants" used in Vietnam to destroy vegetation to make enemy activity easier to see.
Between 1962 and 1971, more than 20 million gallons of Agent Orange were sprayed during the war, contaminating both the ground and soldiers. The International Agency for Research on Cancer reclassified TCDD a group 1 carcinogen in 1997, a classification that also includes arsenic, asbestos and gamma radiation, according to background information with the study.
Dr. Bruce Roth, a professor of medicine and urologic surgery at Vanderbilt University, said he found the study interesting but not persuasive.
"I'm not totally convinced," Roth said, noting that the study relies on self-reported exposure to Agent Orange, without other objective proof of exposure or the amount of exposure.
Roth speculated that because all study participants who reported being exposed to Agent Orange were given thorough screening tests for prostate cancer, more cancers were found. "I can almost guarantee you're going to find more cases of prostate cancer," he said.
"I'm not saying that there is not possibly some relationship, but I don't think that this paper necessarily proves it," Roth said. "But I think you could pick almost any exposure and increase screening, and you are going to find more cases, whether or not the agent is responsible for more cases or not."
Dr. Michael J. Thun, vice president of epidemiology and surveillance research at the American Cancer Society, agreed that the findings were interesting but don't prove a connection between prostate cancer and Agent Orange.
"The finding is provocative, but it's hard to know how to interpret it, unless it can be replicated in other studies," Thun said.
For more on prostate cancer, visit the American Cancer Society.