Abstract 1620: Multiregion spatial sequencing of early-stage head and neck squamous cell carcinoma revealed theranostic intratumor heterogeneity

Abstract Introduction: Head and neck squamous cell carcinoma (HNSCC) is characterized by substantial intratumor heterogeneity (ITH) at the molecular level that may foster tumor evolution, adaptation, and therapeutic failure. Personalized-medicine strategies mostly rely on single tumor-biopsy samples which might not capture the mutational burden of heterogeneous tumors. We investigated genetic ITH portrayed from multiregion spatial sequencing in early-stage HNSCC patients. Patients and Method: Seventy-eight early-stage HNSCC patients treated with upfront curative-intent surgery in the prospective biobanking SCANDARE study (NCT03017573) were included. We developed a pathological measure of ITH, based on the relative contribution of multiple poorly and well-differentiated intratumor regions (n = 199) in resected tumor samples. To characterize genetic ITH, we performed targeted next-generation sequencing on multiple spatially separated intratumor regions by using a custom panel of 571 genes (named DRAGON), in combination with 3’-Tag RNA sequencing and pathway enrichment analysis. Results: Fifty-nine patients displaying a minimum of two sequenced intratumor regions (total, n = 180) were analyzed. We observed genetic ITH in 22/59 patients (37%), of whom 6/22 (27%) based on theranostic molecular alterations. Three of the six patients exhibited molecular alterations in PIK3CA (n = 2) and TSC2 (n = 1) that have supporting clinical evidence of actionability in some cancer types (OncoKB level 1) and three patients exhibited actionable molecular alterations in PTEN (n = 2) and CDKN2A/B (n = 1) supported by substantial research evidence (OncoKB level 4). Two patients exhibited molecular alterations in SMARCA4 that is likely oncogenic, albeit not yet annotated by OncoKB. The pathological measure of ITH accounted for a significant source of variation in gene expression. Notably, we identified 346 differentially expressed genes imposing p-values ≤ 0. 05 and |log fold-change| ≥ 1 involved in several Reactome’s signaling pathways, including the cell junction organization (R-HSA-446728) and the tight junction interaction (R-HSA-420029) pathways. Conclusions: We reported clinically relevant genetic ITH in early-stage HNSCC, which can lead to underestimation of the mutational landscape portrayed from single tumor biopsy and may present major challenges to precision medicine. Our findings uncovered the biology behind ITH and may have translational implications for biomarkers discovery in HNSCC. Citation Format: Grégoire Marret, Sophie Vacher, Constance Lamy, Ladidi Ahmanache, Laura Courtois, Choumouss Kamoun, Maral Halladjian, Zakhia El Beaino, Jerzy Klijanienko, Charlotte Martinat, Emmanuelle Jeannot, Joey Martin, Guillaume Rougier, Nathalie Badois, Maria Lesnik, Antoine Dubray-Vautrin, Olivier Choussy, Wahib Ghanem, Rabah Taouachi, Julien Masliah Planchon, Nicolas Servant, Maud Kamal, Ivan Bièche, Christophe Le Tourneau. Multiregion spatial sequencing of early-stage head and neck squamous cell carcinoma revealed theranostic intratumor heterogeneity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1620.