Abstract B037: Spatial remodeling of the pancreatic tumor microenvironment following chemotherapy and ablative radiotherapy

Abstract

Pancreatic cancer remains highly resistant to therapy, and how chemotherapy, radiotherapy, and targeted therapies remodel the tumor microenvironment (TME) to influence outcomes remains incompletely understood. We hypothesize that treatment-induced changes in the TME can reveal biomarkers of response and identify rational therapeutic combinations. To address this, we previously evaluated patients treated with neoadjuvant chemotherapy (CT) or CT followed by ablative stereotactic radiotherapy (CT+SAbR). In addition to improved pathologic features and local control with CT+SAbR, we identified immune programs associated with favorable local control, including enrichment of CD8 T cells and NK cells, whereas regulatory T cells (Tregs) associated with poorer local control (Leung et al., Clinical Cancer Research, 2025). To further define treatment-induced spatial remodeling, we performed 35-plex imaging using PhenoCycler mulitplex immunofluorescence on untreated (n=3), CT-treated (n=12), and CT+SAbR-treated (n=10) tumors. Using our SPACEMAP platform (Dawod et al., bioRxiv, 2025), we phenotyped and spatially analyzed more than 7 million cells resected specimen of the 25 patients. Although overall cellular composition was not clearly different between the treatment groups, spatial organization differed substantially. We then performed analysis linked to the pathology-annotated tumor bed only. Residual tumor cells after treatment demonstrated increased γH2AX and PD-L1 expression suggesting genotoxic stress and adaptive immune resistance. While therapy reduced overall cytotoxic T-cell abundance and expanded dense fibroblast-rich stromal barriers, CT+SAbR promoted closer spatial association of cytotoxic T cells, macrophages, and dendritic cells with residual tumor epithelium. Ongoing analyses will define treatment-induced immune neighborhoods surrounding persistent epithelial cells and integrate these spatial features with single-cell RNA sequencing to identify molecular pathways associated with antitumor immunity and therapeutic resistance. Together, these studies aim to establish spatial biomarkers of response and nominate rational combination therapies for pancreatic cancer.