HRD in endometrial cancer: LST loss drives distinct genomic profile and platinum response

While homologous recombination deficiency (HRD) presents therapeutic opportunities in endometrial cancer (EC), its molecular determinants and clinical implications remain poorly characterized. Through genomic analysis of 688 cancer-related genes combined with genomic scar assessment, we investigated HRD molecular features and clinical relevance of HRD across three cohorts: an EC cohort from Sun Yat-sen University Cancer Center (SYSUCC, n = 114), the Cancer Genome Atlas EC cohort (n = 500), and a high-grade serous ovarian cancer (HGSOC) cohort (n = 118). HRD was identified in 23.7% of SYSUCC EC cases, and HRD tumors paradoxically had fewer short-nucleotide variations in HRR genes than proficient (HRP) tumors (18.52% vs. 48.28%, P = 0.007). Mechanistic analysis revealed large-scale transition (LST) losses as the potential predominant HRD driver in EC, occurring significantly more frequently in HRD versus HRP tumors (74.1% vs 5.7%; P < 0.001). Comparative genomics demonstrated enrichment of HRR gene LST losses was EC-specific, contrasting with HGSOC where LST distribution was HRD-independent. Clinically, elevated HRD scores predicted reduced progression-free survival (HR 1.74, 95% CI 1.03-2.94; P = 0.04) yet enhanced platinum sensitivity (HR 0.41, 95% CI 0.18-0.94; P = 0.034). Our findings indicate that the HRD phenotype in EC, driven primarily by LST losses rather than short-nucleotide variations, serves as both a prognostic and predictive biomarker.