Background/Objectives: Endometrial cancer is a heterogeneous malignancy that displays distinct molecular features and clinical behaviors. The molecular profile of endometrial cancer and its relationship with menopausal status, histological subtype, tumor grade, mismatch repair (MMR)/microsatellite instability (MSI) status, co-mutation patterns, and TCGA molecular classification were investigated in the current study. Methods: A total of 81 histopathologically confirmed endometrial cancer cases were retrospectively evaluated. Molecular profiling was performed using a targeted 71-gene NGS panel together with MSI-PCR and mismatch repair (MMR) immunohistochemistry. Because the targeted panel was not designed to detect genome-wide copy-number alterations or comprehensive mutational signatures, molecular subgroup assignment was performed using a surrogate TCGA-inspired molecular classification approach based on POLE mutation status, microsatellite instability (MSI)/Mismatch Repair (MMR) findings, and TP53 alterations. Histological subtypes, tumor grades, menopausal status, and molecular alterations were compared. Results: Of the cases evaluated, 57 (70.4%) were endometrioid and 24 (29.6%) were serous carcinoma. TP53 variations were significantly higher in serous carcinomas compared to endometrioid tumors (66.7% vs. 26.3%; p = 0.001). In endometrioid carcinomas, the mean number of variants increased with advancing tumor grade (Grade 1: 4.44; Grade 2: 9.68; Grade 3: 11.42; p = 0.006). Alterations in BLM, CDC27, MLH3, and MSH3 were more frequently observed in high-grade tumors. In exploratory analyses, no significant differences were detected between the premenopausal and postmenopausal groups regarding total variant load, number of altered genes, MSI status, or the distribution of TCGA-inspired molecular subgroups; however, these comparisons were limited by the small number of premenopausal patients. The most frequent co-mutation was observed between BLM and CDC27 (55.6%). In the TCGA-inspired molecular classification, the most prevalent subgroup was NSMP-proxy (33.3%). Conclusions: Serous and endometrioid endometrial cancers display distinct molecular characteristics. In endometrioid carcinomas, the genomic alteration load increases in parallel with advancing tumor grade. TCGA-inspired molecular classification and co-mutation analyses revealed the prominent molecular heterogeneity of endometrial cancer. In exploratory analyses, no significant differences were detected between the premenopausal and postmenopausal groups regarding total variant load, number of altered genes, MSI status, or the distribution of TCGA-inspired molecular subgroups. However, these findings should be interpreted with caution because of the limited number of premenopausal patients. Given the limited number of premenopausal patients, findings related to menopausal status should be considered exploratory and require validation in larger, independent cohorts.

Homologous recombination deficiency (HRD) is a critical indicator of genomic instability; however, the composite HRD score may not reflect the distribution of distinct genomic scar components underlying this phenotype. In this exploratory study, we compared the absolute and relative contributions of loss of heterozygosity (LOH), large-scale state transitions (LST), and telomeric allelic imbalance (TAI) among solid tumors harboring pathogenic or likely pathogenic (P/LP) variants in BRCA1 or BRCA2. This retrospective study included 76 patients with solid tumors who underwent HRD testing between January 2023 and January 2026. P/LP variants in homologous recombination repair (HRR) genes, alongside LOH, LST, and TAI scores, were evaluated. The composite HRD score was calculated as LOH + LST + TAI, with values ≥ 56 defined as HRD-positive. Additionally, the relative contribution of each scar component to the total HRD score was determined. Given the small sizes of the BRCA1-only and BRCA2-only subgroups and the heterogeneity of the overall cohort, all gene-group comparisons were considered exploratory and hypothesis-generating. Overall, 21.1% of the cohort was HRD-positive. Patients harboring BRCA1/2 P/LP variants displayed a significantly higher median HRD score compared to non-carriers (47.0 vs. 30.0; p = 0.016). When comparing patients with tumors harboring BRCA1-only (n = 9) and BRCA2-only (n = 10) P/LP variants, LOH was higher in the BRCA2 group (19.0 vs. 5.0; p = 0.036); however, this difference did not retain statistical significance following false discovery rate (FDR) adjustment (q = 0.108). In an exploratory sensitivity analysis restricted to breast and ovarian tumors (BRCA1-only, n = 5; BRCA2-only, n = 9), the LOH/HRD ratio was higher in the BRCA2 group (0.301 vs. 0.000; p = 0.026; q = 0.039), whereas the LST/HRD ratio was higher in the BRCA1 group (0.488 vs. 0.310; p = 0.019; q = 0.039). These estimates were based on very small subgroups and should therefore be interpreted cautiously. This exploratory analysis identified differences in the relative distributions of LOH and LST between tumors harboring BRCA1-only and BRCA2-only P/LP variants, particularly in the breast/ovarian subset. However, the small and heterogeneous subgroups, together with the absence of systematic assessment of biallelic BRCA1/2 inactivation, preclude gene-specific or mechanistic conclusions. These observations should be regarded as hypothesis-generating and require validation in larger, tumor-specific, independent cohorts.