A number of scientific studies have shown that African-American men are more likely than any other group of men in the world to develop prostate cancer. What's more, they're often stricken at a younger age, and they're more likely to die from the disease.

It's a prime example of a health disparity, which The Minority Health and Health Disparities Research and Education Act of 2000 describes as "a difference in the overall rate of disease incidence, prevalence, morbidity, mortality or survival rates."

Charnita Zeigler-Johnson, Ph.D. '92, wants to know why the differences in prostate cancer rates and time of onset exist in the African-American community.

As a research assistant professor in the University of Pennsylvania's Department of Biostatistics and Epidemiology, Zeigler-Johnson develops
new studies of novel risk factors for prostate cancer.

She then oversees everything that goes along with the studies, such as applying for research funding, training research staff, recruiting study participants, data management, statistical analysis, and writing up the results and having them published.

Zeigler-Johnson started investigating the prostate cancer health disparity in 1999, when she arrived at the University of Pennsylvania to pursue molecular epidemiology training as a post-doctoral fellow. She received a doctorate in epidemiology from the University of Pittsburgh in 1998, having earned a bachelor's degree in psychobiology from Albright.

As part of her fellowship, she managed the "Molecular Epidemiology of Prostate Cancer Study" for Timothy Rebbeck, Ph.D., professor of epidemiology, who leads molecular epidemiologic studies to identify and characterize genes for prostate and breast cancers. She has been working as a member of his research group ever since.

While it's been proven that African-American men have among the highest rates of prostate cancer in the world, Zeigler-Johnson says that other populations of men of African descent are also at high risk. "Even though the rates in sub-Saharan African nations aren't quite as high as what we see in the U.S., some recent studies suggest that they may be higher than previously thought," she said. "And the rates in some Caribbean nations are comparable to what we see among African-Americans.

"Part of that we believe to be genetic," she said, "although we're still trying to find out what that proportion is. We do know that most prostate cancer doesn't seem to have a clear hereditary component.

"It's true that if you have a brother or father, grandfather or uncle who has had prostate cancer you're at higher risk for developing the disease," she explained. "But in our study of prostate cancer cases in the Philadelphia area, just 30 percent of our subjects have a known family history. Two-thirds are sporadic cases."

To help determine how much of a role genetics does play in the incidence of prostate cancer in African-American men, Zeigler-Johnson and her team have been working with African researchers since 2002.

"We were very interested in understanding what was going on with African-American men from a genetic point of view and learning about differences in risk factors," Zeigler-Johnson said. "So we went to both Senegal and Ghana. Right now we have our strongest collaboration with Senegal. We found urologists and health care workers there who helped us begin our work in that area."

Zeigler-Johnson explained that members of her team go to Africa about once a year to meet with those researchers, and they also come to the states. "They have their hands full as urologists, so we assist them with the research side of their work," she said. "We share our database with them, and we'll do statistical analysis if they request our help. We write joint papers, and our collaborators are first author or senior author on some of them. They've actually been the principal investigators on some of the grants."

While working with the African teams, Zeigler-Johnson and her team found that African-Americans typically have a frequency of certain genotypes that's intermediate between Caucasians in the U.S. and African populations.

"That would be expected due to admixture in the African-American population," she said. "We've seen some similarities between African- American men and West Africans with regard to the genotypes that we see. We are currently examining if particular genotypes are associated with prostate cancer in African men."

Since genetic influences have been proven to be just one piece of the puzzle, Zeigler-Johnson's research team has expanded its interests beyond the study of genetics to incorporate race, diet, obesity, smoking, socioeconomic status and neighborhood characteristics.

Of all those factors, Zeigler-Johnson finds neighborhood characteristics particularly intriguing.

"My goal has been to define the risk factors that place all men— and African-American men in particular—at high risk," she said. "So I wanted to focus a little more on some of the factors that hadn't been studied so well.

I decided that neighborhood characteristics can give us some understanding about the socioeconomic conditions in which a person might live, including the types of resources that are near them and whether they have access to those resources.

"There are lots of things we can study in our immediate environments where we live that may influence the chance of a person developing cancer or doing well after being diagnosed with the disease," she said. "And we're finding some interesting things there as we consider the residential neighborhood as a contextual factor."

Zeigler-Johnson and her team have not come to any conclusions at this point, but they have seen some things that have been somewhat consistent throughout their studies. As one might expect, they're considering other avenues as well.

"I've been focusing mostly on socioeconomic status, but there's a lot of research coming out now, especially in obesity, which also has been associated with prostate cancer severity, including poorer outcomes or higher-stage cancer at diagnosis.

"Our results so far have suggested that the relationships between prostate cancer and genes or obesity and other risk factors may be dependent on the context in which they occur. So we're thinking about how all these factors work together to promote health or disease."