The research team, led by investigators analyzing SEER registry data from 2016 to 2021, identified 11,833 women aged 40 and older with microscopically confirmed, malignant primary breast cancer that had already metastasized to bone at diagnosis. The cohort spanned five racial and ethnic groups: non-Hispanic White, non-Hispanic Black, Hispanic, non-Hispanic Asian or Pacific Islander, and non-Hispanic American Indian or Alaska Native. Every patient had known estrogen receptor, progesterone receptor, and HER2 status, known annual household income, and documented history of surgery, chemotherapy, and radiation. After excluding patients with unknown race or male sex, the researchers followed the cohort for cause-specific survival, meaning deaths attributed to the cancer itself.

The statistical approach was rigorous. The team used Kaplan-Meier survival curves with log-rank tests to compare survival between groups, then built multivariate Cox proportional hazards regression models to isolate the independent effect of race while controlling for age, income, molecular subtype, primary tumor site, and treatment history. The models were evaluated at three timepoints: six months, twelve months, and five years after diagnosis. With 5,019 deaths observed in the cohort, the ratio of events to model parameters was large enough to avoid overfitting, and the proportional hazards assumption was formally tested for each covariate, holding for race, the primary variable of interest.

The headline finding was stark. Non-Hispanic Black women had a 24 percent higher hazard of death from breast cancer compared with non-Hispanic White women over five years (hazard ratio 1.241, 95 percent confidence interval 1.145 to 1.345, p less than 0.001). This elevated risk persisted at every timepoint examined: Black women faced a 21 percent higher risk of death at twelve months and a 26 percent higher risk at five years compared with all other racial groups combined. Meanwhile, non-Hispanic Asian or Pacific Islander women actually had better survival than White women (hazard ratio 0.865), while Hispanic women showed no significant difference from the White reference group at five years.

Income mattered too, but in a way that complicated a simple access-to-care narrative. Women with annual household incomes below $75,000 had a 10 percent higher hazard of death than wealthier women (hazard ratio 0.900 for the higher income group, p less than 0.001), and this disadvantage appeared at six months, twelve months, and five years. Age also played a role, with women 65 and older facing a 15 percent higher hazard of death. But the most provocative result emerged when the researchers stratified by income: among women earning $75,000 or more, Black women still had significantly worse survival than all other races, with a hazard ratio of 1.256 at five years. The disparity held among both younger Black women (hazard ratio 1.242) and those 65 and older (hazard ratio 1.318) within this affluent group.

In other words, affluence did not erase the racial gap. Even when Black women had household incomes well above the national median and had received comparable surgery, chemotherapy, or radiation, they died of their disease at higher rates. The same pattern appeared in the lower-income stratum, where Black women faced a hazard ratio of 1.184 at five years. This finding challenges the long-standing assumption that socioeconomic disparities in breast cancer outcomes are primarily a story about access to screening, insurance coverage, or treatment. The authors note that countries with universal healthcare, including Canada, show similar racial disparities in breast cancer outcomes, suggesting that access alone cannot explain the gap.

Treatment itself was powerfully protective across the board. Women who underwent surgical resection of the primary tumor had a 45 percent lower hazard of death (hazard ratio 0.554), those who received chemotherapy had a 58 percent lower hazard (hazard ratio 0.421), and radiation was associated with a modest 6 percent reduction (hazard ratio 0.940). These associations were consistent at all three follow-up intervals, though the magnitude of benefit for surgery and chemotherapy diminished over time. Molecular subtype also strongly predicted survival: the worst outcomes were seen in the rare ER-negative, PR-positive, HER2-negative subtype (hazard ratio 4.880) and in triple-negative disease (hazard ratio 4.159), both relative to the common ER-positive, PR-positive, HER2-negative reference group.

The biology of the disparity is partially, but not fully, explanatory. Black women in the cohort had roughly twice the odds of having triple-negative breast cancer compared with White women (odds ratio 2.04, 95 percent confidence interval 1.74 to 2.39), a finding consistent with a large body of literature linking triple-negative and basal-like tumors to higher prevalence among Black women. Notably, prior research has connected this elevated triple-negative risk to structural racism itself: Black women living in US states with greater structural racism, measured across domains such as educational inequity and disenfranchisement, have higher odds of triple-negative diagnoses than Black women in less discriminatory states. Yet even after adjusting for molecular subtype in the multivariate model, race remained an independent predictor of mortality, indicating that tumor biology alone does not account for the survival gap.

The authors are careful to frame race as a social construct rather than a biological determinant. They argue that the observed disparities should be understood within the broader context of structural determinants of health: residential segregation, unequal distribution of high-quality cancer care facilities, and disparities in insurance coverage have all been identified as contributors to racial gaps in breast cancer outcomes independent of clinical factors. The study also carries important limitations. SEER does not capture comorbidities, performance status, the burden of metastatic disease, the presence of visceral metastases, or details of systemic therapy such as endocrine treatment, CDK4/6 inhibitors, or HER2-targeted agents, all of which could introduce residual confounding. Requiring complete data on income, receptor status, and treatment may also have excluded disadvantaged patients with missing records, introducing selection bias.

Still, the scale and consistency of the findings make them hard to dismiss. Breast cancer survival has improved dramatically in recent decades: women with localized disease now have five-year survival rates approaching 99 percent, while metastatic disease carries a five-year survival of roughly 31 percent. Bone metastases in particular drive substantial morbidity through pathological fractures and spinal cord compression. Yet Black women’s survival gains have lagged behind those of White women by as much as two decades, according to prior research cited in the study. This new analysis demonstrates that even within the metastatic-to-bone population, where prognosis is uniformly poor, race and income carve out meaningful differences in who survives. The authors call for future research to identify the specific structural, biological, or unmeasured clinical factors driving the excess mortality among Black women, arguing that the gap cannot be entirely attributed to late-stage presentation, income, or the treatments captured in national registry data.

Subject of Research: Racial and socioeconomic disparities in survival among women with breast cancer metastatic to bone

Article Title: Race and Socioeconomic Status are Predictors of Survival in Patients With Metastatic Bone Disease Secondary to Breast Cancer

Article References: Castan, A., Dias, R., Mysore, A., Herz, D., Gotoff, K., Kadkoy, Y., Beebe, K., Benevenia, J., & Ippolito, J. (2026). Race and Socioeconomic Status are Predictors of Survival in Patients With Metastatic Bone Disease Secondary to Breast Cancer. Cancer Reports, 9(10), Article e70689. https://doi.org/10.1002/cnr2.70689

Image Credits: AI Generated

DOI: 10.1002/cnr2.70689

Keywords: breast cancer, bone metastasis, health disparities, survival analysis, SEER database, race, socioeconomic status, triple-negative breast cancer, Cox regression, Kaplan-Meier, structural racism, oncology