**5. Conclusions**

This study has shown that some probiotic strains (*L. acidophilus*, *L. casei*, *B. longum,* or *L. rhamnosus* among others) are a valid therapeutic strategy in some common treatmentrelated side effects in adult oncology patients, using both single or multiple strain combinations for at least 4 weeks of treatment. The beneficial variation between the different strains in the selected studies has been similar, which is why all of them represent a possible strategy for complications such as gastrointestinal side effects, immune or inflammatory side effects, and performance status-related side effects. Furthermore, despite its exploratory nature, this study provides some insight into the importance of chemotherapy and radiotherapy, inducing major changes in the composition of microbiota, where these probiotic strains may play an important role to prevent or treat such complications.

#### *Implications for Clinical Practice*

Common treatment-related side effects such as diarrhea, vomiting, mucositis, or abdominal pain are unpleasant for patients who have to undergo chemo- or radiotherapy treatments. Although more research is clearly needed, it has been shown that the gu<sup>t</sup> microbiota plays a key role in immunity, and therefore, probiotics could be considered as a potential therapeutic strategy for treating and preventing these complications in immunocompromised cancer patients. Certain probiotic strains (e.g., *Lactobacillus* or *Bifidobacterium*) have shown to be safe and effective for some of these effects secondary to chemo- and radiotherapy, but also to significantly enhance immune response in these patients. Rather than concluding on this topic, this review provides a common ground to explore more in detail the use of certain probiotic strains for common side effects such as pleural effusions, which have a profound impact on the quality of life and life expectancy of these patients.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/1660-460 1/18/8/4265/s1, Supplementary File 1.

**Author Contributions:** Conceptualization: M.R.-A., A.M.-O., C.R.-P.; methodology: M.R.-A., C.R.- P.; investigation: A.M.-O., L.R.-R., A.F.A., C.R.-P.; validation: M.R.-A., A.M.-O., C.R.-P.; formal analysis: M.R.-A., A.M.-O., C.R.-P.; writing—original draft: M.R.-A., C.R.-P.; writing—review and editing: A.M.-O., L.R.-R., A.F.A.; visualization: A.M.-O., L.R.-R., A.F.A.; supervision: C.R.-P.; project administration: M.R.-A., C.R.-P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The dataset used and/or analyzed in this study is available from the corresponding author on reasonable request.

**Conflicts of Interest:** The authors declare no conflict of interest.
