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BACKGROUND & AIMS: Metastases from gastric adenocarcinoma (GAC) lead to high morbidity and mortality. Developing innovative and effective therapies requires a comprehensive understanding of the tumor and immune biology of advanced GAC. Yet, collecting matched specimens from advanced, treatment-naïve GAC patients poses a significant challenge, limiting the scope of current research, which has predominantly focused on localized tumors. This gap hinders a deeper insight into the metastatic dynamics of GAC. METHODS: We performed in-depth single-cell transcriptome and immune profiling on 68 paired, treatment-naïve, primary-metastatic tumors to delineate alterations in cancer cells and their tumor microenvironment (TME) during metastatic progression. To validate our observations, we conducted comprehensive functional studies both in vitro and in vivo, employing cell lines, multiple PDX and novel mouse models of GAC. RESULTS: Liver and peritoneal metastases exhibited distinct properties in cancer cells and dynamics of TME phenotypes, supporting the notion that cancer cells and their local TMEs co-evolve at metastatic sites. Our study also revealed differential activation of cancer meta-programs across metastases. We observed evasion of cancer cell ferroptosis via GPX4 upregulation during GAC progression. Conditional depletion of Gpx4 or pharmacological inhibition of ferroptosis resistance significantly attenuated tumor growth and metastatic progression. Additionally, ferroptosis-resensitizing treatments augmented the efficacy of CAR T-cell therapy. CONCLUSIONS: This study represents the largest single-cell dataset of metastatic GACs to date. High-resolution mapping of the molecular and cellular dynamics of GAC metastasis has revealed a rationale for targeting ferroptosis defense in combination with CAR T-cell therapy as a novel therapeutic strategy with potential immense clinical implications.
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PURPOSE: Claudin 18 isoform 2 (CLDN18.2) is an emerging biomarker and therapeutic target in gastric and gastroesophageal junction (G/GEJ) adenocarcinoma. This study aimed to obtain deeper understanding of CLDN18.2 positivity patterns, prognostic implications, and associations with various demographic, clinical, and molecular characteristics in G/GEJ adenocarcinoma. METHODS: Archived tumor tissue samples from 304 patients with G/GEJ adenocarcinoma in the United States were assessed for CLDN18.2 positivity by immunohistochemistry. CLDN18.2 positivity was defined as ≥50% or ≥75% of tumor cells with CLDN18 staining intensity ≥2+. CLDN18.2 positivity patterns were analyzed for association with prognosis and clinicopathologic/demographic characteristics. Where possible, CLDN18.2 positivity was analyzed for matched tissue samples to assess concordance between primary and metastatic tumors and concordance before and after chemotherapy. RESULTS: The overall prevalence of CLDN18.2-positive tumors (with ≥75% cutoff) was 44.4% (n = 135 of 304). CLDN18.2-positive tumors had a prevalence of 51.4% (n = 91 of 177) in gastric and 34.6% (n = 44 of 127) in GEJ adenocarcinoma. With a ≥50% cutoff, the prevalence of CLDN18.2-positive tumors was 64.4% (n = 114 of 177) in gastric adenocarcinoma and 44.9% (n = 57 of 127) in GEJ adenocarcinoma. There was no association between overall survival and CLDN18.2 positivity using either threshold. Statistically significant associations were noted between CLDN18.2 positivity and sex, histologic type of G/GEJ adenocarcinoma, and adenocarcinoma subtype (≥75% cutoff), and metastasis site and tumor grade (≥50% cutoff). The overall concordance of CLDN18.2 positivity (≥75% cutoff) was 73% (27 of 37) for matched primary versus metastatic tumor samples and 74% (29 of 39) for matched samples before and after chemotherapy. CONCLUSION: This study demonstrated that CLDN18.2 positivity did not correlate with survival in G/GEJ adenocarcinoma, consistent with published data. On the basis of matched sample analysis, CLDN18.2 appears to demonstrate >70% concordance as a biomarker. Observed correlations with certain patient/tumor characteristics warrant further study.