Abstract
4174 Background: Immune checkpoint blockade (ICB) has limited activity in genomically unselected patients (pts) with PDAC. While anti-tumor activity with combination SABR/ICB has been shown, biomarkers of response are poorly defined. We conducted a phase 1/2 study of PD-L1 inhibitor Durvalumab (D) and SABR after induction chemotherapy in LA and BR PDAC (NCT03245541). We report long-term outcomes and correlative biospecimen analyses. Methods: A multi-institutional, single arm phase 1/2 trial was conducted at Cedars-Sinai and Memorial Sloan Kettering. Initial clinical data reported by Tuli et al, ASCO 2023. Pre-treatment tissue assessed for p40 and GATA3 to determine classical vs basal subtype by immunohistochemistry. Tissue interrogated by immunofluorescence for PD-L1 expression and infiltration of immune cell subsets. Multiparametric immunophenotyping of peripheral blood mononuclear cells (PBMCs) by flow cytometry conducted on baseline and on treatment samples. Wilcoxon rank sum test used to determine difference in biomarkers from each timepoint; p-value <0.05 significant. Results: N= 36 enrolled from 08/2017-05/2022; N=31(86%) LA, N=5 (14%) BR. N= 9 (25%) underwent resection; all R0. At median follow up 36.5 months, 6- and 12-month PFS 69%, 36%. Median PFS 8.7m (95% CI 6.1-14), median OS 16m (95% CI 13-26). N=2 (6%) alive without disease progression. Correlative analyses summarized (table). Key findings; Classical/basal subtyping feasible on N=9 (8 classical, 1 basal). Median PD-L1 score not associated with survival. Peri-tumoral, but not intratumoral CD8+ cells associated with PFS >6 months. Flow cytometry feasible for 70 samples from N=35. Frequency of pre-treatment non-naïve CD4+ FoxP3+ Treg associated with PFS >12. CD103+ CD8+ T Cells significantly expanded on treatment only in patients with PFS>12m (p=0.038) and were significantly enriched relative to PFS<12m on treatment. Conclusions: A proportion of pts with LA PDAC achieve durable control with D and SABR after induction chemotherapy. Baseline peri-tumoral CD8+ cells and peripheral CD103+ CD8 T cells and CD4+ Treg in PBMCs at baseline and on treatment may predict for benefit. Further analyses ongoing and validation in larger cohorts is warranted. Clinical trial information: NCT03245541 . [Table: see text]
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