Background:

African Americans (AA) have a higher mortality associated with breast cancer when compared to Caucasians (C).This has been attributed to diverse factors that include access to care, reproductive factors and different somatic genomic profiles. We aimed to compare the racial mutational landscape of 565 breast
cancer samples.

Objectives and Methods:

• Hypothesis: there are differences in the mutational landscape of breast cancer based on race
• Cross-sectional retrospective study of biomarker data obtained
  from de-identified 565 breast cancer samples
• Sample testing: Multiplatform profiling at Caris Life Sciences:
  • IHC: Immunohistochemistry using FFPE samples – 20 protein
    panel
  • ISH: Fluorescence/Chromogenic in situ hybridization
    (FISH/CISH) – 4 gene panel
  • DNA Sequencing (NGS or Sanger) for somatic mutations:
    Illumina MiSeq platform (Illumina TruSeq Amplicon Cancer
    Hotspot panel, 47 gene) and NextSeq (Agilent SureSelect XT,
    592 gene selected based on COSMIC database

Conclusions:

• Racial differences were found in the molecular landscape of breast cancer, including PIK3CA mutations, AR
  expression and CNV
• Protein expression by IHC revealed lower expression of AR in A
• PIK3CA mutations were overall less prevalent in AA; there
  were also differences on the location of PIK3CA
  mutations when comparing AA to C
• CCND1, FGF4 and FGF19 excess of copies in AA suggest
  11q13 region abnormality
• Our data support racial molecular differences in breast
  cancer that can be explored in future studies