Abstract PO2-09-05: Building genomic and transcriptomic data among African American and Black patients with triple-negative inflammatory breast cancer

Abstract Background: Inflammatory breast cancer (IBC) is an aggressive breast cancer associated with poor response and early metastases. It represents a health disparity, with higher incidence and worse outcomes in Black compared to White patients. Further, IBC is enriched for the more aggressive triple-negative receptor subtype, TN-IBC, and this subtype is more prevalent among Black IBC patients. It is critical to identify genetic and molecular features that may guide better treatments for these aggressive cancers across races, and thus imperative to identify and increase racial representation among bioinformatics datasets. We previously performed comprehensive genomic and transcriptomic analyses for TN-IBC patient samples and here examine the differences among self-identified African American or Black (AA/B) and other races among IBC patients. Methods: As previously described, we collected matched blood and baseline tumor samples before treatment from 19 patients with primary TN-IBC. We performed whole exome and RNA sequencing (RNA-Seq) on these samples and compared mutations and differentially expressed genes (DEGs). Results were compared between 3 AA/B patient tissues vs the remaining 16 (Other) cases. Results: Mutations shared by all AA/B patients included amplification of the five most commonly mutated hallmark genes in the complete cohort, ARNT, BCL9, DDR2, FCGR2B and LMNA (all 100% in AA/B patients versus all 50% in the Other cohort). All AA/B patients had a Notch1 mutation (two deletions and one missense mutation, 100% AA/B vs 6% Other (one deletion)). Comparing differentially expressed genes and gene set enrichment analyses of the Broad molecular signatures database (MSigDB) demonstrates the majority of DEGs are downregulated in these AA/B patients. Six of the top 20 downregulated gene sets from the MSigDB C2 group relate to breast cancer subtype and among this TNIBC cohort AA/B tumor expression was downregulated for luminal and normal subtype related genes in multiple gene sets and enriched in the Lien metaplastic related genes. In the MSigDB C5 sets, over half of the top 20 enriched gene ontology sets among AA/B patients related to chromosomes, chromatin, spindle assembly or histone binding, while 16 of the top 20 downregulated enriched sets related to immune function. Multiple KEGG pathways enriched in AA/B cases related to RNA processing and expression and DNA replication and repair. Lastly, hallmark gene sets enriched in AA/B patients were cell cycle related, and targets of Myc, Hedgehog, B-catenin, TGFb, and TNFa via NFKb, while top significantly downregulated sets related to metabolism and immune response. Conclusion: While findings from a small sample size can only be considered hypothesis generating, some patterns emerge from the data among this rare cohort of AA/B TN IBC patients. These tumors appear to be devoid of luminal signals, characterized by cell cycle and chromatin remodeling signals, enriched for signaling typical of stem cell self-renewal, and perhaps more immune-deprived than other TN-IBC. Additional work to build racially diverse IBC transcriptomic data are needed to develop strategies to understand and improve outcomes for these patients. Citation Format: Wencai Ma, Li Zhao, Gayathri Devi, Savitri Krishnamurthy, Larry Coffer, Angela Alexander, Megumi Kai, Xiaoping Wang, Huong Le-Petross, Miral Patel, Bisrat Debeb, Chandra Bartholomeusz, Jianhua Zhang, Xingzhi Song, Andrew Futreal, Naoto Ueno, Rachel Layman, Anthony Lucci, Jing Wang, Wendy Woodward. Building genomic and transcriptomic data among African American and Black patients with triple-negative inflammatory breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-09-05.