A Review on the Efficacy and Safety of Intrathecal Administration of Novel Medications for Leptomeningeal Metastases in Solid Cancers

Leptomeningeal disease (LMD) is a rare and lethal manifestation that may occur in the advanced stages of solid tumors and hematological malignancies. With advances in diagnostic techniques, the detection and confirmation of the presence of LMD have increased. Although its optimal treatment remains a challenge, the use of the intrathecal route for the delivery of novel therapeutics is now considered a promising drug delivery strategy to complement radiation and systemic-based therapies. Although methotrexate, cytarabine, and thiotepa have a long history in the treatment of LMD, other medications have also been shown to be beneficial. In this article, we have reviewed the effects of novel medications administered via the intrathecal route for the treatment of solid tumors. We have searched PubMed, Scopus, and Google Scholar databases till the end of September 2021 using the following keywords: "leptomeningeal disease", "leptomeningeal carcinomatosis", "leptomeningeal metastases", "solid tumors", "solid cancers", and "intrathecal". Our literature findings have uncovered that most studies on LMD, which occurs secondary to solid cancers, are available as ‘case reports’, and few clinical trials have been conducted to date. Single-drug (monotherapy) or combination drug therapy, administered via the intrathecal route, especially in metastatic breast and lung cancer, has been shown to improve patients' symptoms and overall lifespan, while exhibiting a low and acceptable prevalence of side effects. However, judgments/conclusions about the effectiveness and safety of these drugs still require further clinical evaluation.