Histopathological examination is crucial for the diagnosis of PCNSBL, which is characterized by the diffused infiltration of medium-sized round lymphocytes, creating a distinctive “starry sky” appearance, along with high mitotic activity and frequently observed mitotic figures.[20] The MIB1 proliferation index is typically high (99%–100%), reflecting the tumor’s high aggressiveness and rapid growth characteristics. The gene discussed is MIB1; the disease is neoplasm.