The administration of antibiotics compromises the therapeutic efficacy of PD-1 blockade in cancer patients 163; antibiotic treatment leads to a decrease in gut microbiota diversity and an increase in the abundance of Enterocloster clostridioformis, which subsequently downregulates the serum mucosal addressin cell adhesion molecule-1 (MAdCAM-1) level. This evidence concerns the gene MADCAM1 and cancer.