Prognostic and clinicopathologic significance of the tumor–stroma ratio in pure endometrial serous carcinoma

To evaluate the association of stromal proportion with clinicopathological characteristics and survival outcomes in patients with pure endometrial serous carcinoma (ESC). This retrospective cohort study included 62 patients with pure ESC diagnosed between 2013 and 2025. Stromal proportion was assessed on hematoxylin–eosin-stained hysterectomy sections using a predefined 50% cutoff to classify tumors as stroma-low (≤ 50%) or stroma-high (> 50%). Overall survival (OS) and progression-free survival (PFS) were evaluated using Kaplan–Meier analysis and Cox proportional hazards regression. Of the 62 tumors, 43 (69.4%) were classified as stroma-low and 19 (30.6%) as stroma-high. High stromal proportion was significantly associated with advanced FIGO stage ( p = 0.003), lymphovascular space invasion ( p = 0.001), cervical stromal involvement ( p = 0.005), and pathological lymph node metastasis among surgically assessed patients ( p = 0.007). Patients with stroma-high tumors had shorter median OS (32.5 vs. 76.6 months; log-rank p = 0.018) and PFS (14.3 vs. 45.6 months; log-rank p = 0.003). In univariable Cox analysis, high stromal proportion was associated with poorer OS (HR = 2.266, 95% CI: 1.130–4.544; p = 0.021) and PFS (HR = 2.499, 95% CI: 1.314–4.751; p = 0.005). However, these associations were not significant after adjustment for FIGO stage and lymphovascular space invasion (OS: adjusted HR = 1.030, 95% CI: 0.502–2.115; p = 0.935; PFS: adjusted HR = 1.314, 95% CI: 0.653–2.645; p = 0.445). Advanced FIGO stage remained significantly associated with poorer PFS (adjusted HR = 2.755, 95% CI: 1.032–7.352; p = 0.043). High stromal proportion was associated with adverse clinicopathological characteristics and poorer unadjusted survival in pure ESC but was not an independent prognostic factor for OS or PFS. Larger studies using standardized stromal assessment methods are needed to clarify its potential clinical utility.