Significance of Positive Cerebrospinal Fluid Cytology (Leptomeningeal Metastasis) in Central Nervous System Metastasis - A Multicentre Clinicopathological Review.

Leptomeningeal metastases (LM) is a rare but clinically important subtype in central nervous system (CNS) metastasis. Multicentre data was reviewed to detail the epidemiology, clinicopathological associations among patients with positive cerebrospinal fluid cytology (CSF) cytology. Patients with CNS metastasis and clinical data were identified through the Hong Kong Hospital Authority Clinical Data Analysis and Reporting System (CDARS). In total, through 1st January 2000 to 31st December 2024, 38,893 patients with CNS metastasis were retrieved, 1503 had CSF cytology. The most common primary malignancies were lung (54.16%), breast (11.18%) and gastrointestinal (5.66%; colonic: 3.33%, gastric: 1.86%, esophageal: 0.47%). There were 220 (14.64%) patients with positive CSF, they were younger (57.72 years vs. 60.03, p = 0.005), and likely with breast (20.84%, p = 0.016) and lung primaries (16.47%, p = 0.030). The median overall survival (OS) was 113 days. Positive CSF, age > 60 and gastrointestinal primary were correlated with shorter OS (p < 0.05). The inclusion of brain radiotherapy (260 day vs. 82, p < 0.001) and systemic therapy (496 days vs. 61, p < 0.001) for treatment of leptomeningeal metastases was independently associated with longer OS. Positive CSF cytology is a strong independent indicator of poor outcomes. Radiotherapy and systemic therapy improve overall survival for the medium term (6-12 months).