CXCL13 and primary central nervous system lymphoma: In the past decade, several biomarkers measured in the CSF and the vitreous (in the case of vitreoretinal involvement) were investigated as potentially useful for the diagnosis of PCNSL, such as IL-10, IL-6, CXCL13, miRNA 19-21-92a, neopterin, CD19, and MYD88 hotspot mutations [37,38,39,40,41,42,43,44,45,46,47,48,49,50].