People living in big cities are at greater risk of being diagnosed with late-stage cancer than are residents of rural areas, new research from Illinois shows.

But people living in places that fell somewhere in the middle-suburbs and metropolitan areas surrounding cities, as well as big towns-had the lowest risk of late stage cancer diagnosis, Drs. Sara McLafferty of the University of Illinois at Urbana-Champaign and Fahui Wang of Louisiana State University in Baton Rouge found. "The observed pattern of urban disadvantage emphasized the need for more extensive urban-based cancer screening and education programs," they write in their report.

Early cancer diagnosis means a much greater likelihood of successful treatment, the researchers note, but in the US there are substantial differences among different populations in the likelihood of being diagnosed with late-stage cancer. Some research suggests that people who live in rural areas may be more likely to be diagnosed at later stages, McLafferty and Wang say. But while this is a "commonly held" belief, they add, evidence is mixed.

To investigate, the researchers looked at Illinois State Cancer Registry data for 1998-2002 on breast, colorectal, lung and prostate cancers. They examined rates of diagnoses by zip code, which allowed for a "finer grained classification" of the rural or urban nature of a particular area. They divided zip codes into four groups: Chicago City; the Chicago suburbs; smaller cities and suburbs; "large towns" with populations between 10,000 and 50,000 and their surroundings; and rural areas including towns with populations of less than 10,000 and their environs.

For all of the cancers, the researchers found, rates of late-stage diagnosis were highest in the most urbanized part of the state, the city of Chicago. And there was a "clear and remarkably consistent" relationship between urbanization and cancer diagnoses. Rates dropped as areas got more and more rural, although there was a slight increase in risk for very isolated rural areas. People who lived in large towns had the lowest risk of being diagnosed with late-stage cancer.

Once the researchers accounted for socioeconomic factors such as race and income level, as well as physical access to health care, they found the relationship between urbanization and late-stage cancer diagnosis only remained significant for breast and lung cancer. This suggests, they say, that most of the differences observed were due to the age and race of cancer patients as well as their social environment and ease of access to health care.

Simply classifying an area as "rural" or "urban" is likely an oversimplification when it comes to looking into geographic disparities in health, McLafferty and Wang say.

More study is needed to understand why risk is lowest for town-dwellers, they add. "Residents of these smaller urban places may face fewer space-time constraints in accessing cancer screening services than their counterparts in the most rural and urban settings," they suggest. "Whatever its causes, the lower rate of late-stage presentation in these smaller urban places highlights the scope for improvement elsewhere."