BTK and primary central nervous system lymphoma: It has become a research hotspot in recent years to apply new targeted drugs to improve the prognosis of patients with recurrent refractory type CNS lymphoma by studying gene mutations and signal transduction pathways to find new therapeutic targets, such as Bruton tyrosine kinase, mammalian target of rapamycin, immune checkpoint, and phosphatidylinositol 3-kinase inhibitors, and immunomodulators, have been used in the treatment of recurrent, refractory primary CNS diffuse large B-cell lymphoma.[17]