*Review* **Probiotic Supplements on Oncology Patients' Treatment-Related Side Effects: A Systematic Review of Randomized Controlled Trials**

**Miguel Rodriguez-Arrastia 1,2, Adrian Martinez-Ortigosa 3, Lola Rueda-Ruzafa 4,\*, Ana Folch Ayora 1,2 and Carmen Ropero-Padilla 1,2**


**Abstract:** Cancer affects more than 19.3 million people and has become the second leading cause of death worldwide. Chemo- and radiotherapy, the most common procedures in these patients, often produce unpleasant treatment-related side effects that have a direct impact on the quality of life of these patients. However, innovative therapeutic strategies such as probiotics are being implemented to manage these complications. Thus, this study aimed to evaluate the efficacy of probiotics supplements as a therapeutic strategy in adult oncology treatment-related side effects. A systematic review of randomized controlled trials was conducted in PubMed, Scielo, ProQuest and OVID databases up to and including January 2021, following the PRISMA guidelines. The quality of the included studies was assessed by the Jadad Scale. Twenty clinical trials published between 1988 and 2020 were included in this review. Seventeen studies (85%) revealed predominantly positive results when using probiotics to reduce the incidence of treatment-related side effects in oncology patients, while three studies (15%) reported no impact in their findings. This study sheds some light on the significance of chemotherapy and radiotherapy in altering the composition of gu<sup>t</sup> microbiota, where probiotic strains may play an important role in preventing or mitigating treatment-related side effects.

**Keywords:** drug therapy; gu<sup>t</sup> microbiota; neoplasms; probiotics; radiotherapy; systematic review
