Spatial transcriptomic analysis of the ImmunoADAPT trial: Neoadjuvant endocrine therapy combined with palbociclib and avelumab in early-stage ER-positive breast cancer.

e12624 Background: Pre-clinical studies show that CDK4/6 inhibitors can synergize with PD-(L)1 inhibitors via upregulating adaptive immune system responses. Patients with early stage ER+ breast cancer were treated with endocrine therapy (ET) and avelumab with or without palbociclib (PETA v ETA) under the ImmunoADAPT trial (NCT03573648). The objective response rates were 42.9% vs. 11.1%, PETA v ETA. We report results from the correlative analysis of samples collected during treatment. Methods: This is a phase II pilot study including participants with stage II/III ER+, HER2-negative breast cancer, randomized 2:1 to receive either neoadjuvant PETA or ETA. Avelumab was added at C2D1 to both arms. Breast tissue samples were collected at baseline (BL), C2D1 (C2) and end-of-treatment (EOT). PETA arm participant samples are analyzed by timepoint and response using the 10x Visium Platform for FFPE. Cell type annotations were done with the label transfer function using a published breast cancer cohort. Differential expression (DE) analysis was performed using the MAST test. False discovery rate was controlled at 5% using the Benjamini-Hochberg procedure. All analyses were done using R v4.3.1. Single-cell resolution results using imaging mass cytometry will be reported at the meeting. Results: Samples from 6 participants in the PETA arm are analyzed, including 3 responders (R) and 3 non-responders (NR). T-cell enriched Visium spots of the C2 samples exhibited significantly DE genes related with antigen (Ag) presentation (log2FC, B2M 3.7, CD74 1.8), T cell recruitment (CCL5 4.3), T cell activation (CD24 3.9) compared with BL. This trend was maintained at the EOT v BL comparison, however, not seen in the EOT v C2 comparison. T cell enriched spots of R also exhibited DE genes related with Ag presentation, T cell recruitment, activation and memory at C2 compared with NR, however, not at BL or EOT. Cancer cell-enriched spots exhibited a non-significant decrease in Ki67 gene expression at C2 and EOT compared with BL, and also increased Ag presentation signatures at C2. Cancer cell spots of R had a significantly positive DE of CCND1 at BL compared with NR (log2FC 0.3), which was reversed at C2 (log2FC -1). Ag presentation signatures were also positively DE in R compared with NR at C2 (log2FC, B2M 0.7, CD74 0.6) but not at BL or EOT. A significant upregulation of MYC in the cancer cell spots at EOT compared with BL (log2FC 1.2) and C2 (log2FC 0.9) pointed towards a resistant population encountered at the EOT samples. Conclusions: Our results align with preclinical data showing that CDK4/6 inhibitors can upregulate adaptive immune cascades in the tumor microenvironment, including Ag presentation, T cell recruitment and activation. In our trial, the patients who responded to PETA were the ones who achieved an immune upregulation at C2D1 after treatment with palbociblib+ET. Clinical trial information: NCT03573648 .