Abstract P3-05-02: A minimal DNA-methylation signature to estimate tumor content and molecular subtype in breast cancer tissue samples with potential application to liquid biopsy

Introduction: Breast cancer (BC) is a heterogeneous disease characterized by different molecular "intrinsic" subtypes (PAM50) with distinct prognostic and therapeutic implications. DNA methylation (DNAm) is one of the most studied epigenetic mechanisms involved in BC tumorigenesis and progression. Recently, many studies have demonstrated the capability of DNAm-based assays in detecting and monitoring the disease in liquid biopsy samples from patients with BC, thus confirming promising role of DNAm-based biomarkers in the context of precision oncology. Here we present a novel computational method that exploits a minimal set of informative, clonal DNAm sites to estimate tumor content and molecular subtype in BC tissue samples with potential application for liquid biopsy analyses. Methods: DNAm data of TCGA-BRCA comprising 737 tumor samples, including 135 Basal-like (Basal), 46 HER2-enriched (HER2e) and 556 Luminal A/B (LumA/B) samples, and 96 normal tissue samples were downloaded from GDC Data Portal. To estimate tumor purity, we selected DNAm sites based on the following characteristics: (1) AUC>0.8 or AUC350 samples, high accuracy was obtained for LumA/B and Basal samples while HER2e samples showed lower F1-score due to a drop of recall, though obtaining precision >80% in both datasets. Based on these results, a DNAm-based targeted-seq assay has been designed and will be applied to a series of plasma samples from patients with metastatic BC collected within our center. First results of the assay will be presented during the meeting. Citation Format: Dario Romagnoli, Francesca Galardi, Francesca De Luca, Chiara Biagioni, Erica Moretti, Laura Biganzoli, Ilenia Migliaccio, Luca Malorni, Matteo Benelli. A minimal DNA-methylation signature to estimate tumor content and molecular subtype in breast cancer tissue samples with potential application to liquid biopsy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-05-02.