Reasons for breast cancer disparity multifaceted

CDC: Breast cancer mortality higher in black women
CDC: Breast cancer mortality higher in black women

Lower five-year breast cancer survival rates among blacks compared with whites is more strongly associated with patient presentation characteristics at diagnosis than subsequent treatment, researchers have found.

The difference in five-year survival rates among the two groups dropped from 12.9 percentage points (95% CI: 11.5-14.5) among those matched by age, year of diagnosis and clinical site to 4.4 points (95% CI: 2.8-5.8) after additional matching based on presentation characteristics such as comorbidities and tumor type, Jeffrey Silber, MD, PhD, of Children's Hospital of Philadelphia, and colleagues reported in the Journal of the American Medical Association.

Matching patients based on treatments received cut the difference in survival rates even further to 3.6% (95% CI 2.3-4.9), indicating disparity in treatment quality accounted for less than 0.8% of the overall 12.9% difference.

“These differences in survival appear primarily related to presentation characteristics at diagnosis rather than treatment differences,” commented study leader Jeffrey H. Silber, MD, PhD, of the Children's Hospital of Philadelphia, and colleagues.

Racial disparities in health outcomes, including breast cancer survival, have been well known for decades, with blacks generally faring worse than whites. However, specific factors accounting for these differences have been unclear. 

To better understand this issue, Silber and colleagues examined breast cancer diagnoses and treatment trends using data from Surveillance, Epidemiology, and End Results (SEER)-Medicare databases at 16 U.S. sites from 1991 through 2005.

Data from 7,375 black women were matched with three sets of 7,375 white women on the basis of demographics, patient characteristics at presentation and treatment. Patients had a mean age of 76 years at diagnosis.

Five-year survival rates in the comparison in which patients where matched by demographics only were 55.9% among black patients versus 68.8% in white patients (P<0.001), the researchers found. But when patients were matched by characteristics at presentation, five-year survival fell to 60.8% among whites.

Notable differences in quality of treatment were observed between races. Black patients were less likely to receive breast-conserving surgery plus radiation (14.5% vs. 16.5%) or chemotherapy with a taxane (3.7% vs. 5%) than white women, and were more likely to receive no treatment at all (12.6% vs. 5.9%; P-values of less than 0.001 for all). Yet these differences appeared to have less influence on survival than differences at presentation, the researchers  noted.

One reason for the disparity may be inferior primary and preventive care among black patients in the six to 18 months prior to breast cancer diagnosis, according to the researchers.

White patients were more likely to have received any primary care than blacks (87% in presentation-matched whites and 88.5% in demographic-matched whites vs. 80.5% in blacks), any breast cancer screening (31% and 35.7% vs. 23.5%) any cholesterol screening (38% and 38.2% vs. 33.7%) and any colon cancer screening (21.3% and 23.7% vs. 16.5%; P<0.001 for all).

Another explanation may be greater prevalence of comorbidities among black patients at presentation, including diabetes (26% vs. 15.3%) and congestive heart failure (9.6% vs. 5.9%, P<0.001 for both).

Black patients were also less likely than white patients to have estrogen receptor-positive tumors (53% vs. 64.5%, P<0.001).

“Most of the difference is explained by poorer health of black patients at diagnosis, with more advanced disease, worse biological features of the disease, and more comorbid conditions,” Silbert and colleagues wrote.

In an accompanying editorial Jeanne Mandelblatt, MD, of Georgetown University in Washington, D.C., and colleagues, pointed out several flaws in the study design, noting lack of detailed data on chemotherapy and hormone therapy regimens, but said the overall conclusion was likely correct.

"Ultimately, for any cancer control strategy to succeed, improved care quality appears to be a necessary, but not sufficient condition to eliminate race-based mortality differences in the United States," they wrote.


References

  1. Silber JH et al. JAMA 2013;310(4): 389-397.
  2. Mandelblatt J et al. JAMA. 2013; 310(4): 376-377.
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