The present invention relates to methods and compositions for reducing the risk of cancer relapse in a subject who has received cancer treatment. It is based, at least in part, on the discovery that a restricted fraction of the gut microbiota, including the bacteria Streptococcus anginosus, Parvimonas micra, Acidaminococcus intestini, Eubacterium limosum, Clostridium glycyrrhizinilyticum, Desulfosporosinus lacus, Eubacterium biforme, Anaerofustis stercorihominis, Pseudoramibacter alactolyticus, Peptococcus niger, Armatimonas rosea, Saccharofermentans acetigenes, Finegoldia magna, Levyella massiliensis, Gallicola barnesae, Murdochiella asaccharolytica, and Eubacterium brachy are associated with a reduced risk of cancer relapse.
