Interventional SR is a classic and well-known type of review that aims to assess and compare treatment options. The purpose is to summarize evidence regarding the effects of health care or social interventions for certain diseases or conditions. Ideally, it should be performed including randomized clinical trials (RCT) because of its high level of evidence. If there is a lack of RCT, non-RCT studies or observational studies can be included, however the level of evidence is lowered (8).

To illustrate the strategy for a SR of intervention, we can cite the article by Normando et al. (9) which aimed to assess the effects of turmeric and curcumin for oral mucositis. The authors used the acronyms PICOS with detailed explanation to formulate a precise research question (Table 1). Applying this strategy, the study showed strong evidence for the application of turmeric and curcumin in the treatment of chemo/radio induced oral mucositis. Both turmeric and curcumin were able to reduce pain, erythema intensity, ulceration area, and degree of severity of oral mucositis. They were also effective in prevention by delaying the onset of the lesions. However, the authors suggest further investigation to improve and confirm de evidence.

Diagnostic tests are used by health professionals to discriminate whether an individual has a particular disease or condition in populations considered to be suspect for the disease (10). It is known that a test is sensitive when it can discriminate among suspects, those who are effectively ill. Sensitivity is the reason of the number of true positive assessments per number of all positive assessments. Differently, specificity is the ability of the same test to be negative, which represents the reason of the number of true negative assessments per number of all negative assessments (11). The SR of diagnostic test allows investigating the validity of an index test compared to a reference test (reference standard), considering different designs of diagnostic studies and different population profiles (10). Thus, the SR of diagnosis is a very important tool to study the applications of new exams and diagnostic methods, taking in consideration accuracy, sensitivity, and specificity measures.

As an example, Guerra et al. (12) aimed to assess the capability of serum biomarkers to diagnose HNC. For this purpose, the acronyms PIRDS were applied with detailed explanations (Table 2). The study was able to demonstrate promising serum biomarkers in the diagnosis of HNC. Accuracy was improved by the combination of EGFR + Cyclin D1 and SCCA + EGFR + Cyclin D1. The results have also shown higher sensitivity and specificity when compared to isolated biomarkers. The authors pointed out the need for further well-structured research to validate these biomarkers.

The SR of prognosis is an excellent tool and widely used in HSC field as it is the most adequate review to summarize overall outcomes. It is also used to determine the importance of an exam to determine the prognosis and to identify prognostic factors and predictors of an individual's response to treatment, associated or not with changes in health outcomes (13).

Illustrating this type of SR, Dourado et al. (14) evaluated the impact of cancer-associated fibroblasts (CAF) on oral cancer prognosis. The focused question was structured using a PICOS strategy with detailed information (Table 3). Based on that, authors (14) found CAF as an appropriate prognostic biomarker and therapeutic target in oral cancer. The high expression of CAF was associated with worse overall survival and disease-free survival in oral cancer. Moreover, a correlation of the abundance of CAF and the clinicopathological features could be suggested reflecting in aggressiveness and dissemination of this disease.

In vitro experiments with cell culture and in vivo animal models are studies widely used in the research routine of pathology and histology laboratories. SR with these types of studies provide an excellent source for identifying gaps in the translational research, gaining knowledge and ideas to improve laboratory questions. However, it should be noted that SR of in vitro and in vivo animal studies present a lower level of evidence compared to clinical and observational studies (15). Although there are limitations associated to in vitro and in vivo SR, it is often necessary to answer about specific topics or when there is no stronger evidence available.

Aiming to assess curcumin as an alternative treatment for HNC, Borges et al. (16) conducted a SR with in vitro and in vivo studies. Note that the decision to incorporate laboratory studies was driven by the recognition of the lack of evidence on this topic in a clinical context. The focused question was based on a PICOS acronyms (Table 4). In this study, the authors found curcumin as an effective inhibitor of proliferation and survival in HNC cells. The SR also demonstrated its effects on reducing tumor measurements in animal models. While this SR provides an initial level of evidence, it reinforces the potential of curcumin as an adjuvant drug in HNC treatment. The immediate application of these findings to patients may not be feasible, but it supports the initiation of clinical trials based on fundamental evidence.

SR from epidemiological studies is necessary to regulate health conditions trends in terms of prevalence and incidence. This type of SR can also determine the frequency of clinical, radiographic, or histological findings as signals or symptoms of certain diseases. Data synthesis provided by this type of review is a powerful tool to inform social and healthcare professionals, policymakers, and consumers on the decisions-making moment (17).

As an example of SR of prevalence in HNC, we can cite the article by Moura et al. (18). This review serves as a model for frequency surveys regarding pathway mutations. It aimed to define the prevalence of PI3K-AKT-mTOR signaling pathway mutations in patients with HNC. Using the PEOS strategy to formulation a focused question (Table 5), the authors found an estimated mutations prevalence ranging from 2% (AKT) to 13% (PIK3CA) for the related genes. To make the evidence more robust, they could also perform subgroup analysis according to risk factors and tumor characteristics, including HPV infection, tobacco use, alcohol exposure, TNM stage, and histological tumor differentiation. Moreover, the findings demonstrated that PI3K-AKT-mTOR pathway emerges as a potential prognostic factor and could offer a molecular basis for future studies on therapeutic targeting in HNC patients.

SR of association and risk factors assess individuals' characteristics or habits, such as genetic aspects or environmental exposure, and the risk of developing health conditions. The risk factors can be modifiable, for example, cigarette smoke, or non-modifiable – family history (19). Therefore, SR in this field presents important evidence that influences health practice, not only for professional's care decisions, but also for population counselling.

The SR published by Mello et al. (20) is a model of association review using the PECOS strategy (Table 6). This study aimed to answer if there is an association between mate consumption and the occurrence of upper aerodigestive tract (UADT) cancer. As results, they found an increased chance of cancer occurrence in all UADT subsites (oral, pharynx, esophagus, and larynx) when mate consumption was present. Secondary outcomes showed that high volumes of mate consumption per day increased odds of developing UADT; however, the temperature of consumption did not impact its occurrence.