That finding, suggested by transcriptomic analyses of a racially diverse cohort that identified racial disparities in the proportion of HR-positive basal tumors, underscores a need for diverse racial representation in clinical trials, researchers recently reported at the annual meeting of the American Society of Clinical Oncology.
The leading cause of cancer-associated death among Black women is breast cancer, and compared with White women, Black women are 41% more likely to die from breast cancer, said Sonya A. Reid, MD, MPH, a medical oncologist with the Vanderbilt-Ingram Cancer Center, Nashville, Tenn., and the study author.
Few studies, Dr. Reid said, have evaluated if tumor biology differences contribute to the racial outcome disparity. Hormone receptor-positive tumors classified as basal-type with Blueprint genomic analysis (HR+/Basal) are overrepresented among Black women. These tumors are thought to be similar to triple negative breast cancer tumors (TNBC) which are more aggressive and tend to have worse outcomes.
TNBC, Dr. Reid said, is associated with low ACKR1 expression, which encodes the Duffy antigen and correlates with worse breast cancer outcomes. Given the overrepresentation and worse outcomes among Black women with HR-positive basal tumors, Dr. Reid and colleagues compared differentially expressed genes (DEGs) by race and subtype.
Their analysis of data from 2,657 women with stage 1, 2, and 3 breast cancer, showed that among 455 Black women, 315 had luminal (HR-positive luminal) and 140 had basal tumors (66 HR-positive basal and 74 HR-negative basal). Among White women included as a reference group (n = 2,202), tumors were were HR-positive luminal in 1,825 and HR-positive basal or HR-negative basal in 158 and 219, respectively. The proportion of Black women with HR-positive basal tumors was significantly higher, compared with White women (15% versus 7%; P <0.001) as was the proportion of Black women with HR-negative basal tumors, compared with White women (16% versus 10%; P <0.001).
Women included in the study were participants in the ongoing BEST study (5R01CA204819) at Vanderbilt University Medical Center, Nashvlile, Tenn., or FLEX study (NCT03053193). In a multidimensional scaling analysis, HR-positive basal tumors clustered with TNBC rather than with HR-positive luminal tumors. While a differential gene expression analysis comparing HR-positive basal with HR-positive luminal tumors resulted in over 700 differently expressed genes in Black women, no such genes were identified when comparing HR-positive basal tumors with TNBC. ACKR1 expression in HR-positive basal tumors was comparable to TNBC in Black women (P = 0.81) and White women (P = 0.46). In contrast, HR-positive basal tumors had significantly lower ACKR1 expression than HR-positive luminal tumors in Black (P < 0.01) and White women (P < 0.01).
The findings highlight the importance of further genomic classification for patients with HR-positive tumors, Dr. Reid said.
“Molecular subtype classification is not standard of care for patients with localized breast cancer. However, the current analysis suggests that genomic classification could have important clinical implications. Women with HR-positive basal tumors should not be treated uniformly with HR-poisitive luminal tumors. Our data suggest that HR-positive basal tumors are transcriptomically similar to TNBC tumors and should potentially be treated similar to TNBC,” she said.
There are several genomic tests that are widely available clinically to guide treatment decisions and are covered by insurance, Dr. Reid said. Prior studies have shown racial disparity in the omission of genomic tests to guide treatment decisions, however. “Increasing access [to] and awareness of genomic testing will improve guideline-adherent care for all patients. We must intentionally recruit minority patients into clinical trials, knowing that Black women are more likely to die of their breast cancer,” she said.
A further impediment lies in the fact that while most minority patients receive their care in the community, most clinical trials are offered at large academic centers, Dr. Reid said. Future trials, she urged, should include a predetermined percentage of racial/ethnic groups in the clinical trial design to reflect the breast cancer population.
Limitations of the study included that race was self-reported. She noted further that the data for survival are not yet mature. She added, “We will also be evaluating the association of different systemic treatment options across the different molecular subtypes.”
Dr. Reid reported no relevant disclosures.