Low Relative Dose Intensity During First-Line Chemotherapy for Epithelial Ovarian Cancer: Predictors and Association with Survival in a Single-Center Cohort

Background and Objectives: Relative dose intensity (RDI) reflects how closely chemotherapy follows the planned dose and schedule. We aimed to identify pretreatment factors associated with low RDI during first-line chemotherapy for epithelial ovarian cancer (EOC) and to examine the relationship between RDI and survival. Materials and Methods: This single-center retrospective cohort included 355 patients with EOC who received first-line platinum-based chemotherapy between 2015 and 2025. Mean RDI was calculated from taxane and platinum RDI, with low RDI defined as <85%. Logistic regression was used to identify related factors and construct a nomogram, which was internally validated by 1000 bootstrap resamples. Progression-free survival (PFS) and overall survival (OS) were evaluated using Kaplan–Meier analysis, multivariable Cox regression, and a 6-month landmark analysis. Results: Low RDI occurred in 128 patients (36.1%). Higher BMI category, bilateral/multifocal tumor distribution, baseline neutropenia, and lower prognostic nutritional index were independently associated with low RDI. The nomogram showed an apparent AUC of 0.726 (95% CI: 0.670–0.782) and a bootstrap-corrected AUC of 0.719. After multivariable adjustment, low RDI remained associated with shorter PFS (adjusted HR = 2.234, 95% CI: 1.466–3.405) and OS (adjusted HR = 3.074, 95% CI: 1.658–5.700). The landmark analysis showed a similar pattern. Conclusions: Low RDI may reflect greater treatment vulnerability and difficulty in completing first-line chemotherapy according to the planned dose and schedule. Pretreatment risk assessment may help identify patients who need closer monitoring, while external validation of the nomogram remains necessary.