Screening and diagnosis may be trickier in obese men

PROSTATE CANCER
Doctors often use a prostate cancer marker, called PSA, to help screen patients who might be at risk for developing the cancer. However, a growing body of evidence suggests that screening with the PSA seems to be trickier for obese men than men of normal weight. Recently, several groups have suggested that obese people have lower levels of PSA in their blood, potentially making interpretation of the PSA screen difficult. No one has proposed a convincing explanation for why PSA should drop with obesity. The prevailing idea has been that since obese individuals have lower testosterone, they end up having less PSA levels into the blood. A new study from the Duke Medical Center challenges this theory. Dr. Lionel L. Bañez and Dr. Stephen J. Freedland, both from Duke, believe that the answer lies in the known fact that obese individuals have more plasma, or the liquid component of blood, in their bodies. Since plasma increases with obesity, the relative level of PSA in the blood drops. To study whether such blood dilution might be responsible for low PSA in obese individuals, the authors sampled nearly 14,000 men with prostate cancer with varying body mass indexes, a measure of weight compared to height. Using BMI, the researchers found that men with larger plasma volumes had lower PSA levels - suggesting that obesity probably drops PSA levels because of blood dilution.

BOTTOM LINE: "Our study suggests that tumor markers, particularly PSA, are diluted in obese people. If we don't take this into account, we could be missing cancers in this population," Freedland said.

CAUTIONS: "We only looked at men with prostate cancer," Freedland said, suggesting that the authors need to see whether blood dilution affects PSA levels in men without prostate cancer.

WHAT'S NEXT: The authors need to perform follow-up studies to confirm their findings before applying them to clinical practice.

WHERE TO FIND IT: Journal of the American Medical Association, Nov. 21

SUSHRUT JANGI

ENVIRONMENT

Arsenic is a metal commonly found in the earth's crust. When it makes its way into drinking water, however, it poses serious health risks, including the development of cancer. A new study, led by Mathuros Ruchirawat of the Chulabhorn Research Institute in Thailand and Leona Samson of the MIT Center for Environmental Health Sciences, investigated a district in Thailand with high levels of arsenic in the drinking water. In particular, they examined how exposure of women to arsenic might affect the genes of their children - as arsenic is known to cross into the baby's blood. Researchers found that babies born to exposed mothers had changes in the activity of their genes - babies were more likely to have certain genes turned on and others genes turned off. Arsenic seemed to "reprogram" a group of about 450 such genes, many of these associated with stress, inflammation, and cell growth, potentially making it more likely for exposed babies to develop cancer in the long term. By screening for these genes in the future, it may be easier to determine which individuals have a higher risk for disease - allowing doctors to target those at risk with careful health monitoring and therapy.

BOTTOM LINE: Arsenic exposure may reprogram certain genes leading to an increased likelihood of health consequences, such as the development of cancer. The identification of these genes, however, may help determine which individuals are most likely at risk for the development of disease.

CAUTIONS: "We don't know whether these genetic changes are specific to arsenic," says first author Rebecca Fry from MIT. For example, metals other than arsenic may cause similar genetic changes as well.

WHAT'S NEXT: "The babies who were part of the study are now toddlers and we are now following this population for long term health consequences," says Fry. The group also plans to determine how the identified genes might help predict arsenic exposure in babies.

WHERE TO FIND IT: PLoS Genetics, Nov. 23.

SUSHRUT JANGI