We evaluated the diagnostic potential of lymphocyte‐specific protein tyrosine kinase (LCK) as a biomarker in differentiating primary central nervous system lymphoma (PCNSL) from glioblastoma multiforme (GBM) using bioinformatics analysis (Gene Expression Profiling Interactive Analysis, The Cancer Proteome Atlas, Tumor Immune Estimation Resource, GEO, Oncomine) and immunohistochemistry. The gene discussed is LCK; the disease is neoplasm.