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Breast Cancer Outcomes Show Ties to Neighborhood Income in New Study

NEW YORK – For patients with estrogen receptor-positive breast cancer, income levels appear to have nuanced associations with everything from the risk of disease recurrence to likelihood of survival, new research suggests, pointing to a potential socioeconomic impact on tumor biology.

"We have known that income level increases the incidence of poor-prognosis triple-negative breast cancer, but this is the first data to show that income level impacts survival even in breast cancer with a better prognosis," senior and corresponding author Anurag Singh, director of radiation research at Roswell Park Comprehensive Cancer Center and co-leader of the center's cancer stress biology program, said in a statement.

As they reported in JAMA Network Open on Tuesday, the researchers from the Roswell Park Comprehensive Cancer Center, the University of Buffalo, and the University of Florida analyzed data for 119,478 women with early-stage estrogen-receptor (ER)-positive breast cancer, diagnosed between 2006 and 2018, looking at whether expression-based 21-gene recurrence scores (RS) or overall survival patterns varied in relation to a patient's household income level, extrapolated from neighborhood level data.

"Despite extensive research in the roles of socioeconomic inequalities and breast cancer disparities, there is a paucity of studies evaluating the association of socioeconomic status with intrinsic tumor biology," Singh and his coauthors reasoned.

The team's analyses suggested that breast cancer patients living in zip codes with an average household income below $50,353 tended to have higher RS than patients from more affluent neighborhoods — a relationship that was not found when considering education level, another socioeconomic indicator.

Nearly 69 percent of the participants fell in the higher income group, living in neighborhoods above the average US household income, and just over 31 percent were in the lower income group by neighborhood.

When it came to survival, meanwhile, the researchers reported that low income corresponded with poorer overall survival, but only in the subset of individuals with 21-gene RS that fell below 26 on a scale of 0 to 100.

"Given the lack of patient-level income data, our findings may not be generalizable to individual patients from different socioeconomic backgrounds within the same zip code," the authors cautioned.

The researchers also emphasized that the potential mechanisms underlying income-tumor biology relationships reflected in these RS and overall survival patterns are yet to be determined. Even so, they had some theories.

"Low income levels may lead to less cancer screening with consequent delay in diagnosis and worsening of tumor biology," the researchers explained, noting further that "financial distress has been shown to result in increased psychological and emotional distress" that may, in turn, bump up stress-related pathways with ties to tumor biology.

Such hypotheses may also help to explain prior studies suggesting that the tricky-to-treat triple-negative subtype of breast cancer is overrepresented in individuals classified as low income.

In contrast, the team explained, past results indicate that chemotherapy responses tend to be relatively poor in individuals in the high RS group, perhaps explaining why the income effect did not seem to correspond with overall survival in breast cancer patients with 21-gene signature scores of 26 or higher.

"In our observational cohort study, low household income was independently associated with higher RS and worse survival outcomes among those with RS below 26, but not RS 26 or higher," the authors concluded, noting that "[f]urther studies are warranted to investigate the mechanism behind the association between socioeconomic determinants of health and intrinsic tumor biology among patients with breast cancer."