Clinical outcomes and prognostic factors of Ommaya reservoir-based intrathecal chemotherapy in lung cancer leptomeningeal metastasis: a retrospective cohort study

Objectives To evaluate clinical outcomes and identify prognostic determinants in patients with lung cancer leptomeningeal metastasis (LCLM) treated with Ommaya reservoir-based intrathecal (IT) chemotherapy. Method We retrospectively reviewed 154 LCLM patients treated at Fudan University Shanghai Cancer Center (2022-2025). All patients underwent Ommaya reservoir implantation, or combined with VP shunt. IT pemetrexed (30 mg/week) was delivered for 4–6 consecutive weeks. Clinical characteristics, cerebrospinal fluid (CSF) and magnetic resonance imaging (MRI) features were collected. Survival outcomes were assessed using Kaplan–Meier and Cox regression analyses. Results The cohort had a median age of 59 years (IQR, 53-65) with predominance of female sex (59.1%), lung adenocarcinoma (98.1%), and EGFR mutations (76.7%). Median overall survival (OS) for the entire cohort was 331 days (IQR, 266–446). To provide guidance on clinical decision making, we established an exploratory four-tier prognostic system integrating KPS and intracranial pressure (ICP), categorizing patients into distinct prognostic quartiles. Our analysis revealed that among patients with Karnofsky Performance Status (KPS) ≥70, a normal ICP was associated with superior survival. Conversely, in patients with KPS ≤ 50, a decrease in intracranial pressure indicates a poorer prognosis for the patients. Multivariate Cox regression identified KPS, extracranial metastasis, MRI morphology, and CSF glucose/protein as independent prognostic factors. A nomogram developed from these variables showed excellent discrimination (AUC = 0.894) and robust calibration. Conclusions This study establishes a practical risk stratification system and a prognostic nomogram to assist individualized clinical decision-making for LCLM patients.