A study of neighborhoods suggests that modifiable factors, not genetics, underlie the racial disparities that have been seen in survival of breast and prostate cancer.

While "large city" studies have shown considerable racial disparities in cancer survival, the new study shows that racial disparities virtually disappear in studies that focus on smaller populations, such as neighborhoods within larger cities.

In their study reported Monday in the journal Cancer, researchers led by Jaymie R. Meliker, of New York's Stony Brook University, asked the question: Do racial disparities in breast and prostate cancer survival seen in large counties persist in small cities and even smaller neighborhoods?

They studied geographic regions in Michigan, using the Michigan Cancer Surveillance Program, which compiled information from 1985 to 2002 on 124,218 breast cancer and 120,615 prostate cancer patients.

As the geographic scale gets smaller, they explain, the population becomes more homogenous in terms of income, access to medical care and other factors that may influence cancer survival. Therefore, the researchers hypothesized that if racial disparities in cancer survival diminished when smaller geographic areas were analyzed, modifiable factors, not genetics, may be responsible for the disparity.

In support of their hypothesis, the study revealed that whites had significantly higher survival rates of prostate and breast cancer compared with blacks when large geographic regions were analyzed. However, when smaller geographic areas were analyzed, such as legislative districts and neighborhoods, disparities diminished or virtually disappeared.

"When racial disparities vanish in small geographic areas, it suggests that modifiable factors are responsible for apparent racial disparities observed at larger geographic scales," Meliker and colleagues write.

It is unclear which modifiable factors are important, but the current findings suggest that genetic factors are not likely to play a large role in disparities of survival from prostate and breast cancer," they conclude.