Off-label use of bevacizumab in age-related macular degeneration: protocol for a systematic review and meta-analysis

Background: Age-related macular degeneration (AMD) is recognized as the leading cause of vision loss in elderly people. Taking into account the phenomenon of aging worldwide, the prevalence of AMD is expected to increase gradually in the future. AMD can be divided into early, intermediate and late stages, where early and intermediate are mainly asymptomatic and, late-stage can be classified in non-vascular AMD and vascular AMD. Current pharmacological treatment in vascular AMD includes the administration of anti-VEGF agents, such as ranibizumab, pegaptanib, and aflibercept. Additionally, it has been reported that the off-label use of bevacizumab, through intravitreal administrations, demonstrates to be effective along with a lower cost in comparison to other agents used, which makes it a new possible pharmacological approach. Objective: This review aims to evaluate the efficacy, safety, and efficiency of the use of bevacizumab in the treatment of neovascular AMD Methods: To identify and select relevant articles present in current literature, it will be developed a highly sensitive search strategy. To develop this search, it will be used MEDLINE via the Pubmed platform. It will be only considered randomized controlled clinical trials, where it


Background
Age-related macular degeneration (AMD) is intimately associated with visual impairment, considered as the leading cause of vision loss in elderly people.(1-3)Indeed, it is reported that 9% of all cases of blindness are related to the progression of this disease.(4)AMD frequency accompanies the advancing age and is known to be a progressive and degenerative disease in the macula.(1,5) It is estimated that around 200 million people are affected with AMD worldwide, and with the phenomenon of aging in the entire world, the prevalence of this disease may increase in a near future.(3)(4)(5)(6) Allied with the increased life expectancy, there are other risk factors identi ed such as environmental factors, obesity, atherosclerosis, smoking, genetic background, metabolic and functional factors.(2,7) AMD can be divided into early, intermediate, and late stages.The early and intermediate stages are mainly asymptomatic and represent about 90% of cases.(6-8)Late AMD is classi ed into two main types, which are non-vascular or dry (atrophic) AMD and neovascular (wet or exudative) AMD, and is the main cause of AMD visual impairment.(2,4,5,8) AMD diagnosis and grading are based on color fundus examination in people ages 50 years and older.(9) There are some differences to be aware of between both main types of AMD, where non-advanced AMD is characterized by typical focal drusen with a whitish-yellow localized between retinal pigment epithelium and bruch membrane (BrMb).On the other hand, wet AMD is known to present neovascularization within the macula.(10) AMD pathogenesis is not fully understood yet but some studies are starting to elucidate the underlying process behind the appearance of this disease.(8,10, 11) Both non-vascular and neovascular AMD are related to a dysfunction and/or death of all constituents of the photoreceptor/retinal pigment epithelium (RPE)/BrMb/choriocapillaris (CC) complex, as they are working in combination.The development of each type of AMD seems to be associated with the location where initiating events start to disenroll.(11) Nonvascular AMD development is characterized, in the beginning, by a formation of large con uent drusen and hyperpigmentation, which can be underlined by RPE dysfunction, carrying a risk for the appearance of geographic atrophy.(11,12) On the other hand, neovascular AMD is associated with an initial loss of choroidal vasculature, which will affect the photoreceptor/RPE/BrMb/CC complex and, appears to be underlined by a reduction in blood supply, induced by stenosis of large vessels.An in ammatory environment establishes with an accumulation of proin ammatory cytokines, promoting the progression of AMD.(11,13) RPE remains intact however, due to the stenosis observed in large vessels, it becomes hypoxic and starts to release angiogenic substances, including vascular endothelial growth factor (VEGF), stimulating the formation of new vessels from CC, denominated as choroidal neovascularization.(11) Taking into account the underlying process behind the development of neovascular AMD, its current pharmacological treatment is characterized by intravitreal administrations of molecules speci cally targeted to VEGF.(4,14) Additionally, the drugs currently accepted by the regulatory authorities, for the treatment of this condition are, for example, pegaptanib, ranibizumab, a ibercept, and brolucizumab.(4,8) Also, it has been reported the off-label use of bevacizumab in the treatment of neovascular AMD, which is a drug commonly used in oncology, and more speci cally, in the treatment of metastatic colorectal cancer, breast and lung cancers.(2,4,14) Indeed, some authors have shown a positive in uence of intravitreal administrations of bevacizumab in cases of neovascular AMD, allied with a lower cost for the community in comparison with other drugs currently used, for example, ranibizumab.(2,14,15) Therefore, given the rise in bevacizumab use in neovascular AMD, it would be interesting to evaluate, more speci cally, its long-term in uence on the development and progression of this disease.In this sense, this study aims to evaluate the use of bevacizumab in the treatment of neovascular AMD, through the analysis of its e cacy, safety, and e ciency pro les from data present in clinical studies made, with special emphasis in long-term results.

Methods/design
The research group has followed the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-analysis Protocols (PRISMA-P) for the elaboration of this protocol in Supplementary Material 1.(16)This study pretends to answer the following research question "When, how and what are the criteria to the treatment with bevacizumab in adults over 50 years old diagnosed with wet macular degeneration?".

Aims
This study aims to undertake a systematic review and meta-analysis of the evidence about the off-label use pro le of bevacizumab in the treatment of neovascular AMD, through the identi cation and critical appraisal of clinical studies.The speci c objectives are to summarise and analyze the evidence on: 1.The criteria that justify the choice of bevacizumab in neovascular AMD; 2. The therapeutic regimens used with bevacizumab in neovascular AMD; 3. The clinical outcomes related to the e cacy, safety, and e ciency resulting from the use of bevacizumab in neovascular AMD.

Types of studies
We will include experimental clinical studies, such as randomized clinical trials, quasi-randomized clinical trials, and controlled clinical trials.Additionally, retrospective and prospective cohort studies, crosssectional, observational studies, and case-control studies will be included as well.

Exclusion criteria
As exclusion criteria, it was established: studies using participants with less than 50 years old, reviews, author letters, case reports, preclinical studies including in vitro and in vivo studies, and studies with participants diagnosed with polypoidal choroidal vasculopathy (PCV) or retinal angiomatous proliferation (RAP).

Participants
According to the natural history of AMD considered by the American Academy of Ophthalmology Preferred Practice Pattern (17), the study will only include participants diagnosed with neovascular AMD aged 50 years and older.

Intervention and comparison
Patients diagnosed with neovascular AMD treated with bevacizumab, administered intravitreally, in comparison to other accepted treatments, such as another anti-VEGF drug, such as ranibizumab, or even a placebo.

Outcomes
To evaluate the in uence of intravitreal administration of bevacizumab in neovascular AMD, there are several outcomes to be analyzed in terms of comparison with other established treatments or placebos, such as: Outcomes for goal 1 -Economic criteria, drug availability/accessibility, and chronicity of neovascularization; Outcomes for goal 2 -Administrated dose, number of administrations, frequency of administration, and duration of treatment; Outcomes for goal 3 -E cacy, measured in visual acuity and retinal thickness; Safety, measured in macular atrophy, endophthalmitis, leakage, increased intraocular pressure; and E ciency, measured in cost vs bene cial effect of the treatments compared with ranibizumab or placebo.

Database and strategy
We will use MEDLINE via the Pubmed to develop our search, utilizing a highly sensitive search strategy to identify and select relevant and eligible studies.Supplementary Material 2 presents the search strategy developed for the MEDLINE database.This search will be directed to studies indexed from 2010 until 2021.

Data extraction and management
The retrieved studies from the Medline database will be exported and analyzed through a Systematic Reviews Web Application (Rayyan QCRI), which will be utilized throughout the review for study screening and overall management.

Study selection
Titles and abstracts of retrieved studies will be screened, and full text of potentially eligible articles assessed by two independent reviewers.In case of discrepancies, a third reviewer will be included to make a nal decision.Inclusion and exclusion criteria will be used throughout this process to decide whether a study is included or excluded.Relevant data will be extracted from eligible studies and inserted in a customized data extraction document, by the two independent reviewers.As inclusion criteria, only studies using a comparator (ranibizumab or placebo) will be of interest.Additionally, in terms of language, it will be only accepted articles written in English and published starting from 2010.

Quality assessment
All the selected studies will be assessed to evaluate their quality and potential for risk of bias by two independent reviewers.In cases of discrepancies between these two reviewers, a third element will arbitrate to make a nal decision.To evaluate the quality and risk for bias in experimental studies, the Critical Appraisal Skills Programme (CASP) Randomised Controlled Trials Checklist, CASP Cohort Study Checklist, and CASP Case-Control Study Checklist will be used.(18-20)Additionally, it will be used the Effective Public Health Practice Project tool, with the same objective previously referred to, but for crosssectional and observational studies.(21) We will derive domain-speci c and overall quality grading for each study as follows: A-low risk of bias; B-moderate risk of bias; C-high risk of bias.We will evaluate the potential for publication bias by using funnel plots and Begg and Egger tests and the Trim and Fill approach to explore the possible in uence of publication bias on the results.

Analysis
The included studies will be descriptively analyzed and presented in a tabular form.In methodologically and statistically homogeneous studies, we will perform meta-analyses using random-effects models to quantify a pooled estimate of the effect of systemic adverse events (SAE) vs ocular adverse (OAE).Meta-analyses will be undertaken separately for each speci c study design.It will also be considered other subgroup analysis, for instance, age groups (50-70, ->70).We will quantify the heterogeneity between studies using the I 2 statistic and Kendal's Tau and if high values were found, to try to explain heterogeneity across studies, a meta-regression will be conducted.This technique can be performed if there is a suspected variable that may lead to differences in treatment effects across studies.For meta-analysis, it will be used the R (version 4.0.5)packages metafor and meta.

Grading of the overall strength of the evidence
To evaluate the quality and strength of the overall evidence, it will be used the approach Grading of Recommendations Assessment, Development, and Evaluation (GRADE).(22) This procedure will be divided in two stages, as recommended by the GRADE system.Firstly, each outcome will be rated on a scale of 1-9, where: punctuation between 7-9 represents an outcome that is critical for clinical decisionmaking; a punctuation between 4-6 represents an outcome that is important but not critical for clinical decision-making and, punctuation between 1-4 represents an outcome that is not important for clinical decision-making and with lower importance to patients.(22) In the second stage, the quality of the overall evidence for each outcome will be reviewed and will be presented using the GRADE evidence pro ling template.

Registration and reporting
The protocol for this review will be submitted and registered with the PROSPERO.The present protocol will be conducted by following the PRISMA-P guidelines for the development of systematic reviews and meta-analysis.In case of modi cations in the protocol, it will be reported in the nal document, including the rationale behind the origin of such amendments.

Discussion
The off-label use of bevacizumab in the treatment of neovascular AMD was rst time reported in 2006, and since then, an increase in its use has been demonstrated as well.(2)Indeed, bevacizumab has been associated as a treatment option for this condition, taking into account the demonstration that its e cacy is non-inferior, in comparison to ranibizumab, a well-known drug used in this context.(23) In this sense, this review will allow a clearer vision of the in uence of bevacizumab in the treatment of neovascular AMD, evaluating its e cacy, safety, and e ciency compared to another drug used or placebo.Additionally, this study presents as key strengths: synthesize the information available about the off-label use of bevacizumab in patients diagnosed with neovascular AMD; clarify the current evidence about the off-label use of bevacizumab in neovascular AMD context, taking into account its e cacy, safety, and e ciency and, the development of a comprehensive and highly sensitive search strategy, which will provide the identi cation of current literature and the underlying evidence existent.

Conclusions
Age-related macular degeneration is intimately associated with blindness and has a signi cant impact on social, health, and economic factors in society.Currently, this disease has no cure and pharmacological treatment aims to slow its rate of development and preventing the major consequence previously referred to, which is blindness.Taking into account the cost of current drug therapies that are accepted for the treatment of neovascular AMD, bevacizumab appears as a possible alternative treatment.With the literature currently available, we are in a position to, objectively, evaluate the in uence of bevacizumab in the treatment of this disease, in comparison to another drug accepted by the regulatory authorities.

List Of Abbreviations
AMD -Age-related macular degeneration BrMB -Bruch membrane CC -Choriocapillaris CASP -Critical appraisal skills programme GRADE -Grading of recommendations assessment, development, and evaluation PROSPERO -International prospective register of systematic reviews OAE -Ocular adverse events PCV -Polypoidal choroidal vasculopathy PRISMA-P -Preferred reporting items for systematic reviews and meta-analysis protocols RPE -Retinal pigment epithelium RAP -Retinal angiomatous proliferation SAE -Systemic adverse events VEGF -Vascular endothelial growth factor Declarations Ethics approval and consent to participate: The study was submitted to the Ethical Council of Escola Superior de Tecnologia da Saúde de Lisboa (ESTeSL) with register number CE-ESTESL-Nº.77-2020 and was approved at November 2020.Consent for publication: Not applicable