Abstract PO4-25-03: Comprehensive immune profiling reveals factors associated with neoadjuvant chemotherapy response in triple negative breast cancer

Abstract Background: KEYNOTE-522 has resulted in FDA approval of the immune checkpoint blocker pembrolizumab with neoadjuvant chemotherapy for patients with high-risk triple negative breast cancer (TNBC), given the remarkable improvement in pCR rate to 65% along with improvement in event free survival, while with chemotherapy alone, the pCR rate is 40-50%. Unfortunately, use of pembrolizumab is associated with several immune related adverse events (irAE), some of which can be life-threatening and debilitating, including cardiomyositis, encephalitis, and adrenal insufficiency, among others. Hence, there is an unmet need to identify biomarkers in the tumor microenvironment which could predict patients who may attain pCR with chemotherapy alone and be spared the side effects from the added PD-1 inhibition. Methods: Comprehensive immune profiling, including PD-L1 IHC and the expression of 395 immune genes by RNA-seq, was performed on 1:2 matched FFPE tumor samples from 23 stage 1-3 TNBC patients (2 stage 1, 6 stage 2, 15 stage 3). All patients were female with an average age of 48 years (range: 25-79 years). 14 patients were treated with neoadjuvant chemotherapy alone (NAC) and 9 were treated with neoadjuvant chemotherapy combined with the checkpoint inhibitor pembrolizumab (NAC+I). mRNA expression signatures of tumor inflammation (TIGS, weak/moderate/strong), cell proliferation (CP, poor/moderate/high), and cancer testis antigen expression burden (CTAB) were determined by RNA-sequencing. Statistical comparisons of quantitative biomarkers between groups were calculated using the Wilcoxon Rank-Sum test, overrepresentation analysis of categorical variables between groups was calculated by proportions test, and survival differences were quantified by Cox proportional hazards analysis. Pathological responses were documented as pathological complete response (pCR) vs. non-pCR. Results: Across the entire cohort, patients with a BMI 30 had significantly higher PD-L1 expression (assessed by RNA) than those with a BMI ³ 30 p=0.047. While not a statistically significant association, the NAC+I group tended to have a higher pCR rate compared to the NAC group 44.4% vs. 28.6%, p=0.66. Across the entire cohort, tumors with high CTA expression, designated as CTAB high, had a higher pCR rate than CTAB low tumors 54.5% vs 16.7%, p=0.089. No significant difference in pCR rate between TIGS or CP groups was detected for the NAC group, but in the NAC+I group, highly proliferative tumors had a lower pCR rate than moderately proliferative tumors 0% vs. 80%, p=0.048. The pCR and non-pCR groups for each treatment type also exhibited distinct gene expression profiles. Among the NAC group, underexpression of FOXP3 and overexpression of MAPK14 and CD44 were associated with pCR p≤0.031, while underexpression of IFNB1, MAPK14, and CD44 was associated with non-pCR p≤0.029. Among the NAC+I group, overexpression of CXCR4, TNFR and CCL20 was associated with non-pCR p≤0.046. Interestingly, SDHA was significantly overexpressed in the non-pCR subset of patients in the NAC group and significantly underexpressed in the non-pCR subset of patients in the NAC+I group p≤0.031. Conclusions: The development of biomarkers of treatment response is essential to the integration of immunotherapy with chemotherapy as a combined cancer treatment. Our study profiled the immune context of both NAC and NAC+I and identified several key microenvironmental differences underlying divergent treatment response in both groups. A comprehensive understanding of these factors could potentially predict pCR to chemotherapy alone, enabling the avoidance of the unnecessary treatment of these tumors with immunotherapy. Citation Format: Robert Seager, Heidi Ko, Sarabjot Pabla, Maria-Fernanda Senosain, Pawel Kalinski, Erik Van Roey, Shuang Gao, Kyle Strickland, Rebecca Previs, Mary Nesline, Stephanie Hastings, Shengle Zhang, Jeffrey Conroy, Taylor Jensen, Marcia Eisenberg, Brian Caveney, Eric Severson, Shakti Ramkissoon, Shipra Gandhi. Comprehensive immune profiling reveals factors associated with neoadjuvant chemotherapy response in triple negative 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 PO4-25-03.