Purpose To explore the clinicopathological features and molecular characteristics of primary CD5+diffuse large B cell lymphoma(DLBCL).Methods Immunohisto-chemistry and next-generation sequencing(NGS)were used to compare the pathological features,immunophenotypes,and mo-lecular characteristics between primary CD5+DLBCL and CD5-DLBCL,and to analyze their relationship with prognosis and clinical characteristics of patients.Results Among 311 DLBCL patients,there were 46 cases(14.7％)of CD5+DLBCL.There were no statistically significant differences in patient gen-der,clinical staging,international prognostic index between CD5+DLBCL and CD5-DLBCL,and between CD5+DLBCL with and without MYD88 L265P mutation(P＞0.05).Immuno-phenotypically,the overexpression of BCL2(69.5％vs 49.4％,P=0.003)and the co-expression of BCL2 and C-MYC(26％vs 14％,P=0.04)were higher in the CD5+DLBCL group than those in the CD5-DLBCL group;the expression of C-MYC(53％vs 20％),BCL6(93.3％vs 61.3％),Ki67(93.3％vs 64.5％),and co-expression(46.7％vs 20.8％)were higher in the CD5+with MYD88 L265P mutation group than those in the CD5+without MYD88 L265P mutation group(P＜0.05).Survival analysis showed that the disease progres-sion-free survival time of patients in the CD5+DLBCL group tended to be shorter than that of patients in the CD5-DLBCL group(P=0.09).Furthermore,the disease progression-free survival time of patients in the CD5+without MYD88 L265P mutation group was significantly longer than that of patients in the CD5+with MYD88 L265P mutation group(P=0.04).NGS detection found differences in the distribution of accompan-ying mutated genes between CD5+DLBCL and CD5-DLBCL groups.ConclusionCD5 expression and CD5+with MYD88 L265P mutation may be potential indicators of poor prognosis in DLBCL patients.