Latest clinical research in leptomeningeal disease (LMD)-a narrative review

Leptomeningeal disease (LMD) is associated with poor survival and health-related quality of life (HRQoL). There is an urgent need for clinical research in this area to improve the outcomes. The purpose of this study is to summarize the areas of active clinical research in LMD, identify the knowledge gap, and suggest future research directions.

A narrative review of clinical trials in LMD was conducted based on a search in clinicatrials.gov using the search term "leptomeningeal" under "condition or disease". Clinical trials in patients with LMD arising from solid malignancy that were labelled as "not yet recruiting", "recruiting", "enrolling by invitation" or "active, not recruiting" were included. Studies which were deemed to have significant impact on future research direction in LMD were selected for discussion.

A total of 38 clinical trials were included. Of these 38 trials, 19 are discussed in this review, with focus on their research questions and impact on future research directions. Most of the studies that were not selected for discussion focused on biomarker-driven interventions. Four key areas of research were identified, namely the (I) diagnosis, response assessment or molecular profiling of LMD (n=2); (II) advances in radiotherapy (n=3); (III) intrathecal treatment (n=13); (IV) novel drug carrier for systemic treatment (n=1). The research questions in the 19 discussed clinical trials included the tumour microenvironment of LMD, the role of novel molecular techniques in LMD, combination of radiotherapy with drugs, and cell-based immunotherapy. Among these 19 studies, 11 were phase 1 trials, 3 were phase 2 or phase 1/2 trials, 2 were phase 3 or phase 2/3 trials and the study phase was not reported in the remaining 3 studies. The existing knowledge gaps are discussed, including the lack of primary site-specific prognostic tools, cost-effectiveness studies, dedicated HRQoL assessment tools for LMD and sequencing of treatment.

The current clinical trials in LMD offer the promise to improve the diagnosis and treatment outcomes of patients with LMD. More research is needed to overcome the potential hurdles in the current treatment and bridge the knowledge gaps as identified in this review, to improve patients' quantity and quality of survival.