35 2 Discussion HR-QoL is often impaired in patients with oral cancer,50 and these patients face challenges in masticatory function caused by the tumor itself or oncological treatment.51 Therefore, this review described the HR-QoL mastication scores in patients treated for oral cancer, as measured with the UW-QoL questionnaire. The UW-QoL mastication scores ranged from 31.9 to 97.4.29,49 However, there was a wide variety in methodology (e.g., patient groups, treatment, assessment moment), making it impossible to compare outcome scores. Strengths and limitations This review is strengthened by the fact that the PRISMA guidelines were followed. Another strength of this review is the use of the UW-QoL questionnaire. This questionnaire has been extensively researched, developed and validated, and is available in several languages.52 Studies utilizing the UW-QoL questionnaire have been selected in an attempt to obtain standardized outcome measures. However, our review shows that there is a wide variety in the way the outcomes of the UW-QoL questionnaire are reported, making it difficult to compare data. Another limitation of this review is the overall quality of the included studies. None of the studies had a prospective calculation of the sample size. In addition, some studies had a small number of patients or did not include all eligible patients in their study. Therefore, we cannot exclude a possible bias introduced by differences in patients that participated in the studies. In addition, there was a large heterogeneity between and within studies, both in demographic-, tumor- and treatment details, and in reported outcomes. Tumor site was too heterogeneous for adequate comparison between studies, despite our restriction to oral cancer. Eight studies were restricted to tongue cancer.24,34,39,40,43,45,49,53 Other studies included several tumor sites within the oral cavity. Due to this heterogeneity, the variation in reported outcomes, and the heterogeneous sub-groups between studies, it was impossible to perform a meta-analysis. Therefore, only a descriptive analysis of the results is provided. In addition, underreporting study details was common across studies, contributing to the inability to compare findings. To quantify this underreporting, the MINORS assessment tool was used.22 This is the best suitable tool to assess methodological quality of non-randomized surgical studies. However, the combined scores as measured with the MINORS assessment tool did not identify the underreporting in studies as such, despite the noticeable flaws. One problem of the assessment tool is that the scores for each item range from 0 to 2, where a score of 1 indicates that something is reported but inaccurate. When all items are reported but inaccurate, this will therefore lead to a total score of 50%. One improvement could be to further specify missing items, to get a more detailed image of methodological shortcomings.