Following colonization of the intestinal epithelium, the bacteria and metabolites that they release may repress tumor progression through cell-cycle arrest, inhibition of proliferation, downregulation of overexpressed cyclins D1 and E1, inhibition of angiogenesis and tumor survival, and finally a decrease in polyamine synthesis that otherwise supports the growth of cancer cells [261,329,330]. This evidence concerns the gene CCND1 and neoplasm.