Greater risk for aggressive breast cancer subtypes in black women may explain survival disparities

Liz Meszaros, MDLinx | August 07, 2017

Young black women are more likely to have triple-negative or basal-like breast cancer, and the higher prevalence of these aggressive subtypes may account for the gap in mortality that has been documented between black and white women with breast cancers, according to results published in the Journal of the National Cancer Institute.


Aggressive subtypes more likely in black women

This may explain survival disparities between black and white women with breast cancers.

“When we look at a more clinically homogeneous group, such as women who have hormone-responsive, HER2-negative disease, we see pretty significant and biologically important differences between black and white women,” said lead author Melissa Troester, PhD, UNC Lineberger member and professor of epidemiology, University of North Carolina Gillings School of Global Public Health, Chapel Hill, NC. “With genomic information, we’re better able to say which patients are likely to have indolent – or slow-growing – disease. And right now, we might mistake some people as having indolent disease, when actually they have a more aggressive tumor.”

Dr. Troester and fellow researchers conducted this study to assess racial differences in PAM50 subtypes in the population based, phase 3 Carolina Breast Cancer study.

The Carolina Breast Cancer Study was launched at UNC-Chapel Hill in 1993, in an effort to better understand why African-American women disproportionately die from breast cancer. To date, researchers have gathered data on over 8,000 women from 44 counties in North Carolina.

From this study, Dr. Troester and colleagues used data and biospecimens to classify 980 invasive breast cancer via RNA expression-based PAM50 subtype and recurrence (ROR) scores. These scores reflect both proliferation and tumor size.

Researchers compared ROR scores and molecular subtypes (luminal A, luminal B, HER2-enriched, and basal-like) according to race and age (≤ 50 years vs > 50 years).

Researchers found a statistically significantly lower frequency of luminal A breast cancer in younger black women compared with younger white women (25.4% vs 42.8%, respectively), and in older black women compared with older white women (33.6% vs 52.1%).

This is not as positive as it seems at first glance, because women with luminal A breast cancer typically have a better overall prognosis.

In black women, however, all other subtype frequencies were higher:

  • Basal-like: case-only odds ratio (OR): 3.11; 95% CI: 2.22, 4.37;
  • Luminal B: OR: 1.45; 95% CI: 1.02, 2.06;
  • HER2-enriched: OR: 2.04; 95% CI: 1.33, 3.13.

“If you look at the group of basal-like breast cancers, the burden of this disease is much higher if you’re young and black,” said Lisa A. Carey, MD, physician-in-chief, NC Cancer Hospital. “We believe this is playing a role in racial disparities in outcomes between young and old, and black and white women with breast cancer.”

In women with HR+/HER2- cancers, the luminal A subtype was less common. Finally, researchers found significantly higher ROR scores in black women.

These results highlight the vital role of genomic testing in women with breast cancer, to further drive precision medicine approaches to treatment.

“If you really have a luminal A, low-risk tumor, and you were hormone receptor-positive and HER2-negative, you could be treated less aggressively, and have different surgical options,” said Dr. Troester. “But if you had these other tumor genomic subtypes, your doctor might consider a more aggressive treatment plan. We can do better to distinguish aggressive and indolent cancers if we use the genomic data that is becoming available.”

This study was supported by the National Institutes of Health and the National Cancer Institute.