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Southerners living in U.S. cancer belt; Vanderbilt-Ingram Cancer Center researchers study causes of malignancy

Jul. 21, 2008, 11:55 AM

The South is known for many things: hot, steamy summers, iced tea laced with sugar and friendly people with a tendency to welcome strangers. But beneath the veneer of Southern hospitality and gracious living lurks a silent killer: cancer.
Vanderbilt-Ingram
Cancer Center
researchers have their own name for the southern region of the
United States
: the "cancer belt."

Brain cancer is one of the most alarming malignancies disproportionately affecting people who live in this cancer hot spot. Glioma, also known as glioblastoma, is lethal. Ninety-five percent of patients die within two years of diagnosis.

"When you look at a map of brain cancer incidence in the
United States
, the Southeast just lights up in red," said Reid Thompson, associate professor and vice-chair of the department of neurological surgery. "When we found this hot spot on the National Cancer Institute‘s mortality maps we realized something unusual is going on in this region."

Thompson and co-investigator Kathleen Egan, formerly of Vanderbilt-Ingram but now on faculty at the H. Lee Moffitt Cancer Center and Research Institute in

Tampa,

Fla., have launched a study to find clues that may explain this southern brain cancer cluster.

Vanderbilt-Ingram, which sits squarely in the center of the cancer belt, is enrolling as many as 1,000 patients in the study with the help of four other cancer centers.

"We’re asking patients about their diets, possible job-related exposure to cancer-causing chemicals, and we’re collecting DNA samples," explained Thompson. "We know there are some genetic markers that are linked to other forms of cancer and they may play a role in brain cancer as well."

Brain cancer isn’t the only cancer taking an unusual toll on Southern populations. Topping the list is lung cancer. Despite decades of warnings about the dangers of cigarette smoking, Southerners continue to smoke more than individuals in other regions of the country.

But it is less easy to determine why people living in the South are developing many other types of cancer at higher rates than folks who live elsewhere. And it doesn’t explain why African Americans are more likely to develop some forms of cancer and are more likely to die from the disease.

So William Blot, professor of medicine, is leading the Southern Community Cohort Study (SCCS), the largest epidemiologic study in history to explore why the South has become the cancer belt and why African Americans experience higher rates of many types of cancer.

Starting with a $28 million grant from the National Cancer Institute, the SCCS hopes to recruit 90,000 people in 12 Southern states to learn about their lifestyles, their family medical histories and their risk factors for cancer and other serious diseases. Two-thirds of the participants will be African-American and many are from rural areas. Nearly 60,000 people already have enrolled.

The SCCS is a collaborative project among Vanderbilt-Ingram,
Meharry
Medical College
and the International Epidemiology Institute,

Rockville,

Md., as well as participating community health centers across the South.

"The study participants form one of the groups at highest risk for cancer that has ever been studied," explained Blot. "Most other investigations have not included large numbers of African Americans and few have included low-income individuals and people from rural parts of the country."

The focus on African Americans is long overdue, since this group has much higher mortality rates for many forms of cancer. Even when the incidence of a certain form of cancer is higher among whites, the survival rate is nearly always lower for blacks.

While lifestyle factors and access to preventive surveillance and treatment play a role in cancer, scientists increasingly are finding genetic differences that may explain some of the disparities.

African American men are far more likely to be diagnosed with prostate cancer than white men, and the death toll is even more alarming, with African Americans more than twice as likely to die from the disease. Researchers recently found a combination of genes that appear to play a role in the aggressive forms of the disease often found among black men.

The skin pigmentation differences associated with race also may play more than a cosmetic role in some forms of cancer. Dark pigmentation may hinder and light skin may help the body’s ability to produce vitamin D.

"It’s been speculated for a number of years that vitamin D may play a protective role in cancer," explained Blot. "Exposure to sunlight helps the body produce vitamin D, so it stands to reason that someone with dark skin may not be getting enough of the vitamin. Our study in the South found roughly half of the African American population had insufficient levels of vitamin D, versus only 10 to 15 percent of the white population."

This search for genetic variables is just one of the reasons the Southern Community Cohort Study includes DNA samples. Each participant is asked for a blood and urine sample. Those who are unwilling to give blood are asked to use a mouth rinse, from which researchers can extract DNA. This database of biologic specimens, stored at Vanderbilt-Ingram, serves as a treasure trove for scientific investigators.

"Collecting those specimens is absolutely critical to the success of this project," Blot explained. "The way biology and medicine are moving, eventually we’re going to be in a world of individualized medicine, individualized treatment and individualized prevention. To do that you really must have biologic information on patients."

Media contact: Dagny Stuart, (615) 936-7245
dagny.stuart@vanderbilt.edu

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