Racial Differences Identified in Breast Cancer Subtypes

Aggressive breast cancer subtypes are more common among young black women compared with their white counterparts, a new study finds.

The investigators analyzed approximately 1000 invasive breast tumors, and compared the findings of commonly used immunohistochemical tests with findings of the prediction analysis of microarray 50 (PAM50) gene expression assay.

Immunohistochemical tests classify breast cancer based on tumors markers, whereas PAM50 classifies tumors in different risk groups and different molecular subtypes based on the tumor’s genomic characteristics.

The results of the study, published in the Journal of the National Cancer Institute, confirmed prior findings that black women were less frequently diagnosed with luminal A breast cancer—–a form of breast cancer with an overall better prognosis––and significantly higher odds of all 3 non-luminal A breast cancer subtypes.

Basal-like breast cancer was 3 times higher among black women compared with white women. For luminal B breast cancer, the odds were 45% higher for black women compared with white women, and twice that for HER2-enriched breast cancer.

“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 author Lisa A. Carey, MD. “We believe this is playing a role in racial disparities in outcomes between young and old, and black and white women with breast cancer.”

Differences were also observed within a clinically defined subtype. Overall, hormone receptor-positive, HER2-negative breast cancer has the best prognosis, but mortality disparities were found to be greatest within this group.

HER2-negative breast cancer tumors were sometimes classified in the more aggressive genomic subtypes among both black and white women. Furthermore, black womens’ tumors were more often classified into aggressive subtypes, on average, and had a higher risk of recurrence, according to the study.

“When we look at a more clinically homogenous group, such as women who have hormone-responsive, HER2-negative disease, we see pretty significant and biologically important differences between black and white women,” lead author Melissa Troester, PhD, said. “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.”

The findings highlight the role of genomic testing in precision medicine, and may help explain the disparities in survival among black women with this subtype of cancer.

“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,” Troester said. “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.”

The study was part of the third phase of the seminal Carolina Breast Cancer Study launched in 1993. Since its launch, the study has gathered data on more than 8000 women from 44 counties in North Carolina. The primary goal of the study is to better understand why back women disproportionately die from breast cancer.