Abstract B073: Organ-specific diversity of tumor immune microenvironment in metastatic pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) that is refractory to treatment frequently leads to extensive systemic and multi-organ metastases. PDAC is characterized as an immune “cold” cancer; however, the persistence of this “cold” tumor immune microenvironment (TIME) across distant metastases, and the mechanisms by which metastases influence their respective TIME, remain poorly understood. In this study, we conducted spatial protein expression profiling of the TIME using the Nanostring GeoMx Digital Spatial Profiling (DSP) platform. We employed a 43- plex panel on 54 tissue samples, including 14 primary tumors and 40 matched metastases from organs commonly affected by PDAC metastases (liver, lung, and peritoneum), obtained through a rapid (“warm”) autopsy program. We quantified protein expression in three cellular compartments: PanCK+ epithelial cells, α-SMA+ fibroblasts, and CD45+ immune cells, across 181 regions of interest (ROIs). Our analysis revealed a significant enrichment of CD45+ immune cells in lung metastases compared to other organ sites, with a notably lower presence of these cells in liver metastases. Focusing on the immune cell compartment, we analyzed the CD45 segments for further investigation. After normalization using housekeeping proteins, including Histone H3, GAPDH, and ribosomal protein S6, we found that the immune profiles were most distinct between liver and lung metastases. Specifically, liver metastases exhibited the greatest deviation in immune profile compared to primary PDAC, lung, and peritoneal metastases. We scored protein expression signatures for various immune cell subsets based on specific marker expressions. When comparing liver to lung metastases, scores for T cells, myeloid cells, checkpoint markers, macrophages, and interferon signaling were significantly lower in the liver, underscoring the immune “coldness” of the liver metastasis environment. Our cohort included six untreated patients and nine patients treated with chemotherapies. We compared protein expressions in each organ site between untreated and treated patients. Notably, treatment induced divergent expression patterns of multiple proteins between liver and lung metastases. While treatment significantly reduced the expression of several immune markers, including CD45 (total immune), CD3 (T cell), CD4 (T helper cell), CD45RO (memory T cell), CD163 (M2 macrophage), and B7-H3 (checkpoint marker), in lung metastases, these markers were significantly upregulated in liver metastases of treated patients. This finding indicates a pronounced divergence in TIME modulation in response to treatment between liver and lung metastases, potentially fostering a treatment-resistant environment in PDAC patients with multi- organ metastasis. Consequently, this urges the need to develop tailored therapeutic strategies for PDAC metastasis, taking into account the distinct immune landscapes of different metastasis sites. Citation Format: Jimin Min, Vittorio Branchi, Kimal I Rajapakshe, Nisha Narayanan, Guangsheng Pei, Linghua Wang, Jean L Grem, Thomas C Caffrey, Paul M Grandgenett, Michael A Hollingsworth, Paola A Guerrero, Anirban Maitra. Organ-specific diversity of tumor immune microenvironment in metastatic pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B073.