Researchers have long known that where you live – near a Superfund site, for instance – can affect your cancer risk.

A new study suggests that who you live with – as in, your neighbors – can affect that risk, as well.

The research, recently published in the journal Cancer, was led by Carolyn Fang, co-leader of the cancer prevention and control program at Fox Chase Cancer Center.

In a review of existing literature, the researchers wound up with a nuanced look at people who live in ethnic enclaves, or other areas that are highly segregated.  Sometimes the effect was positive; sometimes it was negative.

She spoke to us recently about the findings.

What prompted this area of research? 

It's a conundrum. Some research suggests that, for immigrants or racial/ethnic minorities, living in neighborhoods with others from a similar cultural background is associated with lower risk for various chronic diseases.  The reasons why are not fully understood, but it could be because living in such neighborhoods allows immigrants to maintain some of their traditional health behaviors, such as diet.

Also, living in close proximity to other people who share a similar background could foster greater social cohesion or social support, which has health benefits.  It's nice to live in a neighborhood where people know each other and look out for each other.

On the other hand, racially segregated neighborhoods tend to be characterized by socioeconomic disadvantage. And there is abundant data demonstrating that poverty is detrimental to one's health.

So we wanted to explore this question of whether these neighborhoods are advantageous or detrimental with respect to cancer.  The literature suggested that they could be both.

What did you find?

It's complicated.   Some neighborhoods – for example, those with a higher proportion of Hispanic American or Asian American residents – were associated with a lower risk of certain cancers such as colon cancer or breast cancer. On the flip side, those same areas were associated with an increased risk for other cancers, primarily cancers of an infectious origin — cervical and liver cancers.

There could be several reasons why this pattern was observed.  In neighborhoods with a large minority population, social and cultural norms along with community resources – such as neighborhood grocery stores – might help preserve the maintenance of healthier behaviors, such as a less "Westernized" diet. That has been one hypothesis proposed for why living in neighborhoods with a greater proportion of Hispanic or Asian Americans is associated with a lower risk of cancers associated with Western lifestyle factors.

On the other hand, social and cultural beliefs may hinder the uptake of health behaviors, such as participating in cancer screening.  For example, cervical cancer can be detected through routine tests, such as the Pap smear. But among Hispanic and Asian American women, rates of cervical cancer screening are particularly low, which is likely contributing to the higher risk of cervical cancer that was observed.

What about advanced disease and mortality? 

For disease stage and mortality, we found that living in neighborhoods with a higher proportion of Hispanic Americans was associated with greater odds of being diagnosed with more advanced disease.  Looking at mortality, living in neighborhoods with a higher proportion of African American residents was associated with greater mortality.

In several studies, this association was observed regardless of the race or ethnicity of the individual living in those neighborhoods.  As a result, these findings suggest that limited access to care could be contributing to the poor outcomes observed.

However, it is important to bear in mind that not all studies found neighborhood composition to be related to cancer risk, disease stage or mortality. There were a few studies that reported  either no association, or the inverse. That's why I qualify everything with "it's complicated."

It sounds as if many factors may be at work here. 

Multiple factors are likely driving these findings.  Social beliefs and norms can have an impact on various lifestyle behaviors or cancer screening behaviors.

There's also the access issue. If people are uninsured or underinsured, or they don't have transportation to get to the clinic, they are less likely to receive the care that they need, which could result in greater risk of developing cancer or being diagnosed at a later stage.  Or when a cancer is detected, if an individual is not able to access appropriate treatment, that would certainly have an impact on mortality.

What's next? 

One of the next steps my colleagues and I would like to take is to identify key characteristics of these communities that are driving or contributing to these associations.

The findings we reported are at a macro level. We see that living in certain areas might be associated with lower risk or higher risk, better outcomes or worse outcomes, but we don't really know why. We have some hypotheses, so the next step is to dig deeper, to go to a micro level. Is it behavior? Are people not getting screened? Is it access to care? Or doe the overwhelming burden of poverty have biologic effects that even access to care can't overcome?

It's probably not just one pathway;  it's likely multiple pathways. If we can identify what those pathways are, we might have an opportunity to intervene and change the outcomes.

Ultimately, what we're hoping is that this research will create an awareness that there are broader factors – such as the social environment in which we live – that may be associated with health. Greater awareness of these issues will help us develop more effective programs and approaches for improving the health of our communities. That's where we hope to go next.