Background:  Ovarian cancer is the deadliest gynecologic malignancy. Among epithelial subtypes, high-grade serous ovarian carcinoma (HGSOC) is the most prevalent and is associated with a five-year survival rate below 30%. In Brazil, ovarian cancer is the eighth most common cancer, with an estimated 7,310 new cases per year between 2023 and 2025, and accounts for more than 3,000 deaths annually, largely due to late-stage diagnosis and the absence of effective early detection strategies. The standard first-line treatment consists of cytoreductive surgery followed by adjuvant platinum-based chemotherapy. However, patients who do not respond to this regimen have limited therapeutic options. Objectives and Methods: To elucidate the molecular determinants underlying therapeutic resistance in ovarian cancer by generating and analyzing data through an integrated multi-omic approach combining DNA sequencing, bulk and single-nucleus RNA sequencing. For that, the HGSOC patients enrolled at the Brazilian National Cancer Institute (INCA) were classified using Platinum-Free Interval - the time from the last platinum dose to disease progression/relapse, considering first-line therapy. Results: Whole-genome and exome sequencing demonstrated high data quality, with over 75% of samples achieving a minimum coverage of 30X. Exome analysis of 41 patients identified missense variants, frameshift deletions, and nonsense mutations as the predominant alteration types, with single nucleotide polymorphisms being the most frequent variants, notably C>T transitions. TP53 was the most commonly mutated gene (79%), followed by BRCA1 (23%), predominantly affecting DNA repair pathways. Conversely, platinum-resistant tumors were significantly enriched for mutations in the RAS and NOTCH pathways. Bulk transcriptomic analysis revealed that poor responders exhibit a robust molecular signature of extracellular matrix (ECM) remodeling (COL5A3, MMP16, ADAMTS4), alongside increased integrin signaling (ITGA3), and the focal adhesion kinase PTK2. Integration with snRNA-seq data demonstrated that resistance is primarily driven by tumor-intrinsic features, as stromal and immune cell proportions remained similar between clinical groups. However, a distinct malignant cell cluster exclusive to non-responders was identified, displaying high functional WNT signaling activation, which directly correlates with the observed ECM-mediated survival phenotype. Conclusions and Implications: These results support activation of the WNT-ECM-FAK signaling axis as a key mechanism of therapeutic resistance, whereas highly sensitive patients are characterized by enrichment of DNA damage response pathways, particularly homologous recombination and double-strand break repair, marked by high TP53 mutation rates and recurrent alterations in DNA repair genes such as BRCA1. Overall, integrated multi-omic analyses demonstrate that tumor-intrinsic ECM signaling and DNA repair capacity are key determinants of platinum response, with direct implications for patient stratification and therapeutic targeting.

Financial support: Programa Genomas Brasil; CNPq; FAPERJ