Genomic Alterations in Quadruple-Negative Breast Cancer Tumors

Triple-negative breast cancer (TNBC) lacking androgen receptor (AR) expression defines quadruple-negative breast cancer (QNBC), which is characterized by younger age at diagnosis, high Ki-67 index, and high genomic instability, however a comprehensive description of the genomic characteristics remains poorly defined. A total of 54 TNBC cases were categorized as TNBC with 100% AR expression (TNBC AR-100%) or QNBC, TNBC with 0% AR expression (TNBC AR-0%). Clinical, molecular, and genomic parameters, specifically pathogenic/likely pathogenic (P/LP) variants in homologous recombination repair (HRR) and cancer-related pathways were measured and analyzed. The QNBC cohort exhibited a high homologous recombination deficiency (HRD) score and a greater overall incidence of copy number variants (CNVs). QNBC harbored a higher mutation rate in TP53 and MYC signaling pathway than TNBC AR-100% tumors. P/LP variants corresponding to the HRR, PI3K/AKT, and RTK/RAS pathways were exclusively identified in QNBC. These results suggest that, at both molecular and genomic levels, the two groups are distinct, holding QNBC tumors more aggressive characteristics, genomic instability, and particular impairments in HRR and cancer-related pathways. In terms of actionability, these differences could potentially be leveraged through different combinations of therapies.