Abstract P2-08-23: Early intratumoral changes after a single dose of anti-PD-1 treatment in patients with early breast cancer (BC)

Abstract Intro: Despite the growing success of immune checkpoint blockade in BC, the underlying mechanisms of response or resistance to these treatments is still poorly understood. We recently conducted a window-of-opportunity study (BioKey) including 54 patients with early BC (NCT03197389) in which patients were treated with one dose of pembrolizumab 10 ± 4 days before surgery. A tumor biopsy was taken before and after the administration of pembrolizumab. Using single-cell transcriptome profiling, we identified patients with clonotype expansion of PD-1-expressing T-cells after treatment with pembrolizumab (Bassez A, Vos H et al, Nature Medicine 2021). Expansion mainly involved CD8+ T - and CD4+ T cells. We designated these as patients with clonotype expansion or ‘expanders’ (E), whereas patients lacking clonotype expansion were considered ‘non-expanders’ (NE). In this study, we aimed at investigating the association between stromal tumor infiltrating lymphocytes (sTIL) and various immune markers using immunohistochemistry with the E phenotype. Methods: The BioKey trial has 2 cohorts. The first one included 39 treatment-naive patients who were scheduled for upfront surgery. The second cohort included 15 patients with an estimated residual tumor size of at least 1cm on imaging after neo-adjuvant chemotherapy. All molecular subtypes were represented: triple-negative (TN) BC (n= 18, 8 E and 10 NE), HER2-positive BC (n= 5, 1 E and 4 NE) and hormone receptor (HR)-positive/HER2-negative BC (n= 17, 3 E and 14 NE). 7 core biopsies and 5 resection slides were not contributive and were excluded. The expander status of 14 patients was unknown. sTIL were evaluated and immunohistochemical stains (CD3, CD4, CD8, CD68, CD73, FoxP3, Ki67, PD-1 and PD-L1) were performed. Associations between expander status and biomarkers were assessed using firth logistic regressions, adjusting per cohort. Biomarkers were considered as continuous variables and Odds Ratio computed per one unit increase on a non-transformed scale. Given the low number of E in cohort B, subgroup analyses were performed only in cohort A. Results: We observed that 1) higher levels of sTIL, PD-1+ sTIL and FOXP3+ cells in the pre-treatment biopsies, 2) higher levels of sTIL, PD1+ sTIL, PD-L1+, CD3+, CD4+, CD8+, CD68+, FOXP3+ cells and Ki67 in the post-treatment surgical specimen, as well as, 3) higher delta values (surgical specimen - biopsy) of sTIL, CD3+, CD4+, CD8+, CD68+ and Ki67 are associated with the E phenotype (Table 1). With regard to the subgroup analyses, we observed that higher levels of PD-1+ sTIL and CD68+ cells at diagnosis and surgery respectively, as well as higher delta values for CD68+, Ki67 and sTIL were associated with the E phenotype in HR+/HER2- BC, while high levels of FOXP3+ cells and PD-1+ sTILs in the biopsies, high levels of sTIL, CD3+, CD4+, CD8+, CD68+, FOXP3+, PD-1+ sTILs, PD-L1+ and Ki67 as well as higher delta values for PD-L1+ in the resection specimen were associated with the E phenotype in TNBC. Conclusion: We were able to detect associations between various cell populations of the tumor immune microenvironment evaluated before and after a single dose of pembrolizumab and the T-cell expansion phenotype previously defined at the single-cell level. It highlights the possible clinical utility of a biopsy taken early during treatment. Future neo-adjuvant studies will allow the validation of our findings and investigate the association between T-cell expansion and clinical outcomes. Table 1.Association between the various biomarkers and the expanding T-cell phenotypeVariableOdds RatioLower 95% CIUpper 95% CIp-valuePre-treatment. Core biopsyCD31.071.001.160.061CD41.060.981.170.156CD81.130.951.380.161CD681.050.901.230.494CD73.tumor1.070.821.370.609CD73.on sTIL1.010.961.060.713FoxP32.251.394.030.001Ki671.021.001.050.107sTIL1.061.021.140.005PD-1 on sTIL1.731.212.830.001PD-L11.041.011.070.002Post-treatment. Resection specimenCD31.091.031.190.001CD41.151.051.29<0.001CD81.581.192.34<0.001CD681.471.152.15<0.001CD73.tumor1.090.771.520.608CD73.on sTIL1.030.991.080.110FoxP32.051.313.82<0.001Ki671.041.011.070.004sTIL1.081.031.15<0.001PD-1 on sTIL1.641.152.650.004PD-L11.051.021.110.002Delta (resection-biopsy)CD31.071.011.250.029CD41.091.011.280.030CD81.211.021.690.025CD681.221.051.580.007CD73.tumor0.970.731.290.794CD73.on sTIL1.040.991.120.132FoxP31.220.891.810.219Ki671.051.001.130.031sTIL1.071.001.160.046PD-1 on sTIL0.960.701.330.765PD-L11.000.961.040.941 Citation Format: Hanne Vos, Kathleen Lambein, François Richard, Ines Nevelsteen, Ayse Bassez, Diether Lambrechts, Kevin Punie, Hans Wildiers, Giuseppe Floris, Christine Desmedt, Ann Smeets. Early intratumoral changes after a single dose of anti-PD-1 treatment in patients with early breast cancer (BC) [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 P2-08-23.