*Limitations*

That being said, there are some limitations to bear in mind when interpreting the findings of this study. Fifteen of the analyzed studies were not registered, and therefore there may be a risk of reporting bias, whereas these studies are consistent trials on the Jadad Scale. On the other hand, heterogeneity in strains, length of treatment, and population could be confounding factors, and hence, generalizations should be made with caution. As a result of this heterogeneity in strains, interventions, and data collection methods, neither meta-analysis nor meta-regression were considered in this review. Given the small number of studies included, further work is still needed on the clinical position of probiotic supplements in adult oncology treatment-related side effects, in particular to determine the efficacy of individual probiotic strains, which could help to compare strains and lead more closely to preventive approaches.

As a whole, this review contributes to the existing literature, providing evidence of the current clinical position of probiotics supplements for some common treatmentrelated side effects in adult oncology patients. Despite the main findings of these studies concluded in terms of the safety and efficacy of probiotics supplements for the treatment or prevention of these side effects, further research with larger groups, specific strains, and duration of treatment is needed to conclude the beneficial effects for each of these side effects. More broadly, research is needed to determine the effects of individual and combined probiotic strains in order to draw confident conclusions about their benefits for both general oncology treatment-related side effects and specific cancers. Future research will be particularly interesting in determining how the use of probiotics and prebiotics may enhance the beneficial effect of the first to improve therapeutic responses in patients with cancer.
