Obesity and diabetes might mask the onset of prostate cancer in African American men, making it difficult to detect early-stage and treatable prostate cancer in a population of men already prone to aggressive cancer, according to researchers at Vanderbilt University. Their findings examine the link between prostate-specific antigen (PSA) -- a blood marker which at elevated levels indicates the presence of prostate cancer-- and biological markers for obesity and diabetes.
"African-American men, among all racial groups, are more likely to be diagnosed with prostate cancer at an advanced stage and are also more likely to die from prostate cancer," said Jay H. Fowke, Ph.D., M.P.H., an assistant professor of Medicine and cancer epidemiologist at Vanderbilt-Ingram Cancer Center.
According to Fowke, obese men are also more likely to present with prostate cancer at an advanced stage. Most prostate cancer is diagnosed in response to a PSA test, and a high body mass index (BMI) often corresponds with lower blood PSA levels.
"Diabetes and metabolic disturbances associated with insulin regulation are more common among African-Americans compared to Caucasians, and metabolic disorders associated with obesity and diabetes may lower PSA levels and may cause a delay in referring a patient for a biopsy," Fowke said. "This may be in part why we often don't detect prostate cancer in African-American men until it is already fairly advanced."
Given the increasing rates of obesity and diabetes among African-Americans, Fowke and his colleagues sought a better understanding of the relationship between race, metabolic disorders and PSA levels used to detect early-stage prostate cancer.
The researchers examined participants in the Southern Community Cohort Study, a National Cancer Institute-funded initiative that monitors the health of 90,000 men and women between the ages of 40 and 79 throughout the southern United States. The researchers randomly selected 121 African-American men and 121 Caucasian men; each group had the same proportion of obese and overweight men, as determined by their BMI. Study participants had no prior diagnosis of cancer or diabetes.
From each participant's blood sample, the researchers compared PSA levels with the amounts of HbA1c, C-peptide, leptin and adiponectin -- naturally occurring blood-borne molecules that have a biological role in metabolism, insulin activity, or the function of fat cells. Among African-Americans, PSA levels were 50 percent lower among men with higher levels of C-peptide, a biomarker that reliably indicates an increase in insulin. This association was especially prevalent among obese African-American men, Fowke says. PSA levels also declined somewhat among obese Caucasian men with high C-peptide levels, but this relationship was not as strong as it was in the African-American group.
The researchers saw a similar pattern in Caucasian men regarding the diabetes biomarker HbA1c, where PSA levels were 50 percent lower among men with higher levels of HbA1c. PSA levels were not associated with HbA1c in the African-American group, perhaps suggesting that there may be differences between Caucasian and African-American men in the way PSA responds to obesity.
"There are a number of complex components related to obesity and insulin activity, and we are seeing that metabolic disturbances can have an effect on PSA levels," Fowke said. "It doesn't invalidate PSA screenings, but it does demonstrate that we need research to better understand how obesity and diabetes may be affecting our ability to detect early-stage prostate cancer among African-American men at high-risk for advanced prostate cancer."
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