Influence of Statins on the Survival Outcomes of Patients with Diffuse Large B Cell Lymphoma: A Systematic Review and Meta-Analysis

Background Previous studies evaluating the influence of statins on the survival of patients with diffuse large B cell lymphoma (DLBCL) showed inconsistent results. This systematic review and meta-analysis was conducted to investigate whether statin use is correlated with the survival of DLBCL patients. Methods Related cohort studies were obtained by searching PubMed, Embase, Cochrane's Library, and Web of Science databases. Study characteristics and outcome data were extracted independently by two authors. The random-effect model was used for meta-analysis, considering the possible influence of between-study heterogeneity. Results Eight studies involving 9927 patients with DLBCL were included. Results did not show significant associations of statins with overall survival (OS, hazard ratio [HR]: 0.88, 95% confidence interval [CI]: 0.69∼1.11, p=0.27; I2 = 60%) or progression-free survival (PFS, HR: 0.92, 95% CI: 0.72∼1.17, p=0.49; I2 = 23%) in these patients. Subgroup analyses suggested that statin was be associated with survival of DLBCL patients from Asia (HR for OS: 1.19, 95% CI: 0.91∼1.56, p=0.19, I2 = 2%; HR for PFS: 1.13, 95% CI: 0.89∼1.44, p=0.33, I2 = 0%), but was associated with significantly improved survival of patients from Western countries (HR for OS: 0.73, 95% CI: 0.66∼0.81, p < 0.001, I2 = 0%; for PFS, HR: 0.72, 95% CI: 0.53∼0.96, p=0.03, I2 = 0%), which fully explained the heterogeneity (p for subgroup difference <0.05). Variables such as study design, patient age, and study quality were not shown to affect the findings. Conclusions Overall, statins did not affect the survival of patients with DLBCL. However, statin use may be associated with an improved survival rate of DLBCL patients from Western countries.


Introduction
Diffuse large B cell lymphoma (DLBCL) accounts for up to 40% of total non-Hodgkin lymphomas (NHL) [1]. Currently, rituximab-cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) or R-CHOP-like chemoimmunotherapy has become the first-line chemotherapy for patients with DLBCL, with a curative rate of more than 60% [1][2][3]. However, about one third of the patients will still suffer from disease recurrence or relapse, leading to adverse events such as mortality [4,5]. Statins are the most commonly prescribed lipid-lowering drugs, which function by inhibiting the 3-hydroxy-3-methylglutaryl coenzyme-A reductase, a key enzyme of cholesterol synthesis [6]. Besides, further investigations confirmed multiple pharmacological actions besides lipid-lowering, including anti-inflammation, proapoptosis, antiproliferation, immunomodulation, and antimetastasis, suggesting a possible role statin as an anticancer agent [7][8][9]. Indeed, statins have been shown to reduce the incidence of multiple solid tumors and hematological malignancies, including NHL [10,11]. However, the influence of statin use on clinical outcomes of patients with DLBCL remains to be not fully determined. An early in vitro study showed that statins-induced cholesterol depletion may cause conformational changes of CD20 to escape detection by rituximab, thereby impairing the antilymphoma efficacy of rituximab in CD20 + B cell lymphomas [12]. Subsequent observational studies regarding the influence of statins on the prognosis of DLBCL patients showed inconsistent results [13][14][15][16][17][18][19][20]. An early study showed that statins may adversely affect the prognosis of patients with nongerminal center DLBCL [17], while a recent study suggested that concomitant use of statins may improve the survival of DLBCL patients who were treated with R-CHOP [20]. Accordingly, we performed a systematic review and meta-analysis to comprehensively evaluate the influence of statins on the survival of DLBCL patients.

Methods
e preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement [21] was followed in this systematic review and meta-analysis. e methods of analyzing and reporting of the meta-analysis were consistent with the Cochrane's Handbook for Systematic Review and Meta-analysis [22].

Database Search.
We systematically searched the four electronic databases, including PubMed, Embase, Cochrane's Library, and Web of Science using the combined keywords: (1) "3-hydroxy-3-methyl-glutarylCoA reductase inhibitor," statin, statins, atorvastatin, rosuvastatin, fluvastatin, simvastatin, lovastatin, pitavastatin, or pravastatin; (2) lymphoma; and (3) survival, mortality, death, deaths, progression, recurrence, remission, or collapse. We only considered clinical studies, and no restriction was applied to the publication language. e citation lists of the related articles were also screened manually for possible relevant studies. e date of the final database search was January 12, 2022.

Study
Inclusion. e PICOS criteria were followed during the determination of the inclusion criteria. P (patients): adult patients with confirmed diagnosis of DLBCL; I (exposure): patients with statin use as defined by the original studies; C (control): patients without statin use as defined by the original studies; O (outcomes): relative risks for the incidence of overall survival (OS) and/or progression-free survival during follow-up durations.
S (study design): cohort studies, including the retrospective and prospective studies, published as full-length articles.
Reviews: studies including non-DLBCL patients, studies that did not evaluate the influence of statins, or studies that did not report the survival outcomes were removed.

Data Collection and Evaluation of Study Quality.
Database search, data collection, and evaluation of study quality were separately performed by two independent authors. Discussion with the corresponding author was indicated to resolve the disagreements. Data regarding the study information, patient characteristics, details of statin use, follow-up durations, and survival outcomes were collected. Evaluation of study quality was achieved by the Newcastle-Ottawa Scale (NOS) [23]. is scale varies between 1 and 9 stars and assesses the quality of the cohort studies with three domains, including selection of the patients, comparability between patients with and without exposure, and strategies for the validation of the outcomes.

Statistical Methods.
Hazard ratios (HR) and the 95% confidence interval (CI) were used to indicate the relative risk of survival outcomes between statin users and nonusers with DLBCL. If HRs with more than one model of multivariate regression analyses were reported, we collected the most adequately adjusted HR for subsequent analysis. With data of 95% CIs or pP values, standard errors (SEs) of HRs were calculated and HRs were logarithmically transformed to maintain a normal distribution [22]. Between-study heterogeneity was assessed by the Cochrane's Q test and estimation of the I 2 statistic [24]. Typically, an I 2 >50% was considered as the indicator of significant between-study heterogeneity. To minimize the influence of heterogeneity, we used the random-effect model to pool the HR data of each study in a conservative manner [22]. A series of subgroup analyses were conducted to reveal the influences of study characteristics on the associations according to variables such as study design, location, patient age, and study quality scores. e publication bias was assessed with the funnel plots and the Egger's regression test. We applied the RevMan (Version 5.1; Cochrane Collaboration, Oxford, UK) and Stata 12.0 software for the statistics of the meta-analysis. Figure 1 summarizes the process of literature search. In brief, 545 articles were retrieved in the initial database search after excluding the duplications. en, 28 articles were considered to be potentially relevant after excluding 517 irrelevant articles in title and abstract screening. In the final step of full-text review, another 20 studies were excluded according to the reasons listed in Figure 1. Finally, eight cohort studies were identified and included in the meta-analysis [13][14][15][16][17][18][19][20]. [13][14][15][16][17][18][19][20] involving 9927 patients with DLBCL contributed to this meta-analysis. e characteristics of each study are displayed in Table 1. e studies were performed in Switzerland, Japan, the United States, Singapore, Korea, Canada, and Sweden. Two of them were prospective [14,19], while the others were retrospective. All of the studies included patients with DLBCL. In six studies, R-CHOP or R-CHOP-like chemotherapy was the primary treatment [13][14][15][16][17]20], while the other two studies did not specify the details of treatments [18,19]. Statin use was defined as concurrent use via medical charts validation for six studies [13][14][15][16][17]20], while it was defined as previous use before enrollment in two studies [18,19]. Accordingly, 2847 (28.7%) patients were statin users. e mean follow-up durations were 12-77 months, and confounding variables such as age, sex, stage of lymphoma, and performance status were controlled in the multivariate analyses. e NOS for the studies varied between six and nine, which suggested good quality of the included cohort studies ( Table 2).

Publication
Bias. Funnel plots for the outcomes of OS and PFS were symmetrical on visual examination (Figures 4(a) and 4(b)), suggesting low risk of publication biases, which were further confirmed by the results of Egger's regression tests (p � 0.32 and 0.29. respectively).

Discussion
In this meta-analysis, by pooling the results of eight relevant cohort studies, the results showed that overall, statin use did    International Journal of Clinical Practice 5 not seem to significantly affect outcomes of OS or PFS in patients with DLBCL, even limited to studies including patients treated with R-CHOP or R-CHOP-like chemoimmunotherapy. Moreover, subgroup analysis indicated that concurrent statin use may be associated with improved OS and PFS in patients with DLBCL from Western countries, but not in patients from Asia. Taken together, these findings indicate that statin use does not impair the survival of DLBCL but may improve the survival of DLBCL patients from Western countries.
To the best of our knowledge, this is the first metaanalysis evaluating the prognostic influence of statins in patients with DLBCL. An early meta-analysis including five cohort studies showed that statin use did not affect OS in patients with NHL or chronic lymphocytic leukemia (CLL) [11]. However, mixed patients with DLBCL, follicular lymphoma (FL), and CLL were included, and the differences in the course of the diseases and treatment regimens made the results difficult to interpret [11]. Our study included eight up-to-date cohort studies involving patients with DLBCL only, and showed that statin use did not affect the survival outcome in these patients. Sensitivity analysis limited to studies with concomitant statins in patients treated with R-CHOP or R-CHOP-like chemoimmunotherapy showed consistent results. A previous preclinical study showed that statins may compromise the antilymphoma activity of rituximab via inducing conformational changes of CD20 [12]. e results of our metaanalysis confirmed that the findings of the preclinical study may have no significant clinical implications. One possible     [20]. Besides, accumulating evidence in studies of patients with other diseases that were treated with rituximab also showed that concomitant statins did not significantly affect the clinical outcomes, such as in those with FL [25], CLL [26], or rheumatoid arthritis [27]. Collectively, the findings of our meta-analysis showed that statin use does not impair the survival of DLBCL, even with concomitant statin use in patients treated with rituximabrelated chemoimmunotherapy. Interestingly, results of the subgroup analysis showed that the countries of the study may affect the association between statin use and survival of DLBCL, which fully explains the source of the between-study heterogeneity. Particularly, we found that statin use may be associated with improved survival in DLBCL patients from Western countries but not in patients from Asia. ese findings may suggest a possible racial difference for the influence of statin use on outcomes in DLBCL patients. e potential racial difference for the survival of DLBCL was also observed in a recent study, which showed that Hispanics/Latinos had improved survival compared to non-Hispanics [28]. Currently, the potential mechanisms underlying these findings are not known. One explanation is that the possible interfering of satin on the antilymphoma efficacy of rituximab was mediated on cholesterol depletion [12], which may be affected by the level of serum cholesterol. Patients from Western countries generally have higher serum cholesterol levels than patients from Asia [29], which makes them less vulnerable to the interference of statins. Consistently, a previous study showed that low serum cholesterol levels are a predictor of poor prognosis in DLBCL patients [30]. Studies are needed in the future for the validation of these findings and to reveal the underlying mechanisms.
Our study has limitations. Firstly, the number of the included cohorts was small, and the sample sizes were limited. We could not determine the possible influences of some patient or study characteristics on the outcomes, such as gender of the patients, comorbidities, and regimens of chemotherapy. Besides, influences of type, dose, and duration of statin use on the survival of patients with DLBCL remain to be determined. We could not evaluate the possible influences of these factors because related data were rarely reported among the included original studies. In addition, the different countries of the study may not accurately reflect the different races of the patients. Future large-scale prospective cohort studies may be considered for validation. Finally, this meta-analysis is based on observational studies, the results of which may be affected by selection bias, recall bias, and residual confounding factors. Clinical studies may be considered to evaluate the possible survival benefit of statins in DLBCL patients from Western countries.

Conclusions
In conclusion, results of the meta-analysis showed that statin use does not impair the survival of DLBCL, even with concomitant statins in DLBCL patients treated with R-CHOP or R-CHOP-like chemoimmunotherapy. Moreover, concomitant statins may improve the survival of DLBCL patients from Western countries. Clinical studies are needed to validate these findings, and future studies are warranted to clarify the possible underlying mechanisms.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that there are no conflicts of interest.

Authors' Contributions
Yanbing Li and Liqun Zou conceived the study. Yanbing Li and Huijie Zhou conducted literature search, data