**6.4 Biomarkers associated with the gut**

Studies have suggested the association of the bacterial species in the gut with ICI responses. Bacterial species such as *Akkermansia muciniphila* have been observed and correlated with ICI response, whereas species such as *Ruminococcus obeum* have been correlated with resistance [189, 190]. The use of antibiotics prior to ICI treatment was also associated with a shorter overall survival and progression-free survival. As such, it has been suggested that careful consideration should be given when prescribing antibiotics in patients starting ICI treatment [190]. This is still an emerging field of study and further evidence is needed (**Table 4**).



#### **Table 4.**

*Biomarkers associated with the tumor genome, tumor-immune microenvironment, peripheral blood, and gut that predict response to ICI.*
