Introduction. The standard treatment for non-metastatic triple-negative breast cancer (TNBC) is neoadjuvant chemotherapy (NAC) and nearly 50% exhibit pathological complete response (pCR). However, patients with residual disease after NAC are at increased risk for recurrence and death. Prior studies examining the transcriptome of TNBC pre/post-NAC have examined a limited number of genes (<500) in heterogeneous subgroups of TNBC (e.g. LAR and non-LAR). We explored the transcriptome of androgen-receptor (AR) negative (non-LAR) TNBC subtype both pre/post NAC to identify pathways associated with NAC response. Methods. Tumors obtained pre/post NAC from TNBC patients enrolled in the Breast Cancer Genome Guided therapy study (BEAUTY) underwent RNA sequencing and reverse-phase protein array (RPPA). EdgeR was applied for differentially expressed (DE) analysis and regression methods for RPPA. Digital deconvolution method (CIBERSORTx) and TNBC single-cell data were used to obtain cell types. Pathway analysis was carried out using 2972 gene sets and gene set variation analysis (GSVA). Functional enrichment analysis was conducted with significant genes. Results. Of the 44 TNBC patients, 32 patients were excluded from the analysis cohort due to: LAR tumor (6 pts.), non-LAR tumor with pCR (23 pts.), and cell type issues with RNA-seq data (3 pt.). Paired RNA-Seq data were available for 12 TNBC patients (4 with progression <2 years [EP]) and 8 who were progression-free > 4 years [NP]) and paired RPPA data were available for 9 of these 12 patients. Differentially expressed genes, proteins and cell types between EP and NP in post-NAC. We identified 489 genes differentially expressed (DE) between EP and NP (logFC=|2|, FDR < 0.05). Analysis of cytobands from these 489 genes showed an enrichment of genes on chromosome 6p22.1-2 and 17q25.3 regions (enrichment ratio >5; p-value <10E-4). Critical genes identified in the AR- network (p-value < 10E-3) were IL1RN, SLAMF9, KRT81, BHLHE22, B3GALT5, PCP4, TREM1, AQP9, NRTN, and COL2A1.In addition, preliminary results from RPPA data of post-NAC tumors showed astrocytic phosphoprotein (PEA-15), involved in apoptosis, proliferation, glucose metabolism, as well as cell proliferation and Y box binding (YB1) proteins (involved in metastases), were more DE in EP than NP (p < 0.05). CIBERSORTx was applied to estimate the proportions of different cell types in post-NAC tumors. Cancer-associated fibroblasts iCAFs were low and myCAFs are high in EP vs NP. It is known that the cross-talk between CAFs and tumor cells may induce tumor resistance to chemotherapy. Differentially expressed pathways in post and pre-NAC EP tumors. Using genome-wide expression data from the paired 12 tumors and the GSVA method, we obtained individual pathway scores for 2972 pathways. One hundred ninety pathways were downregulated and 61 pathways were upregulated (p-value <= 0.05) in the post-NAC residual disease of EP relative to NP. We further examined these 190 pathways in the paired EPs and found 71% of those pathways were upregulated in the pre-NAC. These 190 downregulated pathways were enriched with FOXO, TGF-beta, PI3k, FGFR1, insulin and others. The 61 upregulated pathways in post-NAC EP tumors were enriched with mismatch repair, purine, tubulin, telomere, polymerase and gap-junction related pathways; 77% of those 61 pathways were downregulated in pre-NAC. Conclusions. Using a comprehensive “omics” approach, we have identified novel cancer and drug response pathways associated with recurrence in AR-TNBC disease. Further work to evaluate these as markers of outcome and potential drug targets is warranted.

Citation Format: Krishna R Kalari, Vera J Suman, Xiaojia Tang, Jason P Sinnwell, Kevin J Thompson, Peter T Vedell, Jodi M Carter, Sarah A McLaughlin, Alvaro Moreno Aspitia, Donald W Northfelt, Richard J Gray, Richard Weinshilboum, Liewei Wang, Judy C Boughey, Matthew Goetz. Multi-omics data shows downregulation of mismatch repair, purin and tublin pathways in AR-negative triple-negative chemotherapy-resistant tumors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-01-05.