Breast Cancer Mortality Gap Still Baffling

WASHINGTON -- The mystery of why black women have higher risk of breast cancer mortality than whites remains just that -- a mystery.

Action Points

  • African-Americans had worse breast cancer survival than other racial/ethnic groups, and had less treatable types of breast cancer.
  • Point out that across tumor subtypes, the survival among African-American women with breast cancer was worse compared with other racial/ethnic groups , so that the survival difference may not attributable to differential subtype diagnosis.


But a study presented here appears to rule out one possible explanation -- differences by race in the genetic subtype of the disease, according to Candyce Kroenke, ScD, of the Kaiser Permanente Division of Research in Oakland, Calif.

In a prospective cohort of 1,643 breast cancer patients, black women were 71% more likely to die of the disease than their white counterparts, confirming previous research, Kroenke told reporters at the annual meeting of the American Association for Cancer Research.

They were also more likely to have difficult-to-treat forms of the disease, she said.

Previous research has been unable to pin down the mortality to difference to obvious social, economic, or cultural barriers, so the spotlight has been turned on genetics, Kroenke said.

But when she and colleagues broke down their sample by the so-called intrinsic subtype -- based on the PAM50 gene panel -- blacks did worse than whites regardless of the genetic subtype, Kroenke said.

"It's still a mystery," she told MedPage Today. "We still don't know."

The PAM50 panel divides breast cancer into four subtypes -- luminal A, luminal B, basal-like, and HER2-enriched -- with different prognoses. Luminal A, for instance, is regarded as the most treatable and has the best outcomes.

The study included 1,213 white women, 132 blacks, 144 Hispanics, and 154 Asian/Pacific Islanders, Kroenke reported. They were followed for a median of 6.2 years, during which 499 died, including 263 deaths from breast cancer.

Analysis showed that, compared with whites, black women had a hazard ratio for death of 1.71, with a 95% confidence interval from 1.02 to 2.86. The other ethnic groups had lower risks than whites, but the differences did not reach statistical significance, Kroenke reported.

Blacks also had a 4-fold higher risk of difficult-to-treat basal-like disease, compared with luminal A, she and colleagues found.

But they also found that, within each subtype, the risk of dying was higher for black women, compared with whites.

Specifically, black women were 2.3 times more likely to die from the luminal A cancer, 2.6 times more likely to die from luminal B disease, 1.3 times more likely to die from the basal-like subtype and 2.4 times more likely to die from the HER2-enriched subtype.

Kroenke cautioned that the study had a relatively small number of participants. "It definitely needs to be repeated in a larger sample," she told MedPage Today.

The investigators are "shedding light" on a long-standing puzzle, commented Giuseppe Giaccone, MD, PhD, of Georgetown Lombardi Comprehensive Cancer Center here, who was not part of the study.

But the findings still don't completely clarify the issue, since the excess mortality occurs across all genetic subtypes of breast cancer, Giaccone said.

"This is not easily explainable," he said, and investigators may have to re-look at social aspects, although "studying the genetics and what is really happening in these tumors is essential if we want to understand what is happening."

He agreed with Kroenke that the study's small sample size means it must be repeated with a larger data set.

The study had support from the NIH. Kroenke is an employee of the Kaiser Permanente Division of Research in Oakland, Calif.

Giaccone did not make any disclosures.

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