Findings of a study investigating the stool microbiome of patients with metastatic renal-cell carcinoma (mRCC) receiving vascular-endothelial growth factor-tyrosine kinase inhibitors (VEGF-TKIs) reveal profound alterations in the microbiota of patients with VEGF-TKI-induced diarrhoea. Patients with diarrhoea had higher levels of Bacteroides spp and lower levels of Prevotella spp than those receiving VEGF-TKIs who did not have diarrhoea. These findings highlight that alterations in faecal microbiota might explain the VEGF-TKI-induced diarrhoea experienced by some, but not all patients receiving this treatment.