Objective:To investigate the level of serum lipoprotein a [Lp (a)] in patients with diffuse large B-cell lymphoma (DLBCL) and its clinical significance.Methods:A retrospective cohort study was performed. The clinical data of 87 patients with DLBCL who were treated at Changshu No.2 People's Hospital from January 2017 to June 2022 (the newly treated DLBCL group) were retrospectively analyzed, and 78 healthy physical examination subjects were selected as the control group. The level of Lp(a) in the two groups and the level of Lp(a) in DLBCL patients achieving different therapeutic effects after treatment were compared. The receiver operating characteristic (ROC) curve was used to analyze the efficacy of serum Lp(a) in predicting the therapeutic effect of DLBCL patients, and the area under the curve (AUC) was calculated to determine the optimal critical value. Based on the optimal critical value, patients with DLBCL were divided into low Lp(a) group and high Lp(a) group, and the clinicopathological characteristics of DLBCL patients with different Lp(a) levels were compared. Cox proportional hazards model was used to analyze the factors affecting the prognosis of DLBCL patients. Kaplan-Meier method was used to compare the relapse-free survival (RFS) and overall survival (OS) of DLBCL patients with different Lp(a) levels.Results:The level of Lp (a) in the newly treated DLBCL group was higher than that in the control group[ (0.24±0.09) g/L vs. (0.09±0.06) g/L], and the difference was statistically significant ( t = 3.61, P = 0.019). Among 87 patients, 54 achieved complete remission (CR), 23 achieved partial remission (PR), and 10 achieved progression of the disease (PD). The Lp (a) levels of patients achieving CR, PR, and PD were (0.09±0.09) g/L, (0.12±0.08) g/L, and (0.25±0.15) g/L, respectively. The Lp (a) levels in patients achieving CR and PR were lower than those in the newly treated DLBCL patients [(0.24±0.09) g/L], and the differences were statistically significant (all P < 0.05). There was no statistically significant difference in the Lp (a) levels between patients achieving PD and the newly treated DLBCL patients ( P > 0.05). The ROC curve results showed that the optimal critical value of serum Lp (a) in predicting the efficacy of DLBCL patients was 0.25 g/L, AUC was 0.776 (95% CI: 0.676-0.876, P < 0.05), and its sensitivity and specificity was 66.67%, 82.76%, respectively. According to the optimal critical value of Lp (a) (0.25 g/L), patients were divided into the low Lp (a) group (≤ 0.25 g/L) (57 cases) and the high Lp (a) group (>0.25 g/L) (30 cases). The proportion of patients with lactate dehydrogenase level >227 U/L, Ann Arbor stage Ⅲ-Ⅳ, and extranodal organ involvement >1 in the high Lp (a) group was higher than that in the low Lp (a) group, and the differences were statistically significant (all P < 0.05). Cox multivariate analysis results showed that Ann Arbor stage Ⅲ-Ⅳ, international prognostic index (IPI) score 3-5, and Lp (a)>0.25 g/L were independent risk factors for OS in DLBCL patients (all P < 0.05); Ann Arbor stage Ⅲ-Ⅳ and IPI score 3-5 were independent risk factors for RFS in DLBCL patients (all P < 0.05). The median OS in the low Lp (a) group was not reached; the median OS of the high Lp (a) group was 21 months, and there was a statistically significant difference in OS between the two groups ( P = 0.001). The median RFS time was not reached in the low Lp (a) group and the high Lp (a) group; and there was no statistically significant difference in RFS between the two groups ( P = 0.102) . Conclusions:Lp(a) level of DLBCL patients is increased, and Lp(a) could be a factor influencing the prognosis of DLBCL.