Table 1.

Evidence for tumour-promoting effects of the bacterial microbiota

Cancer type	Disease or model	Findings	Refs
Murine studies
Colorectal cancer	Germ-free rats and spontaneous carcinogenesis	Fewer tumours in germ-free rats	23
	Germ-free rats and DMH-induced	Fewer tumours in germ-free rats	25
	Germ-free rats and AOM-induced	More tumours in germ-free rats	28
	Germ-free rats and MAM-GlcUA	Fewer tumours in germ-free rats	28
	Germ-free rats and AOM-induced	Fewer tumours in germ-free rats	32
	AOM in Il10−/− gnotobiotic mice	Fewer tumours in germ-free mice	29
	Germ-free ApcMin/+ mice	Fewer tumours in germ-free mice	31
	ApcMin/+ Cdx2–Cre mice treated with antibiotic cocktail	Fewer tumours in antibiotic-treated mice	36
	Nod1−/− mice treated with antibiotic cocktail	Fewer tumours in antibiotic-treated mice	34
	AOM plus DSS -treated mice treated with antibiotic cocktail	Fewer tumours in antibiotic-treated mice	37
	Wild-type microbiota transplanted into Nod2−/− mice	Fewer tumours after transplant	78
Gastric cancer	Helicobacter pylori-infected gnotobiotic INS-GAS mice	Fewer tumours in germ-free mice	30
	H. pylori-infected INS-GAS mice, treated with antibiotic	Fewer tumours in antibiotic-treated mice	38
Liver cancer	DEN plus CCl4-treated germ-free mice	Fewer tumours in germ-free mice	21
	DEN plus CCl4-treated mice, receiving antibiotic cocktail	Fewer tumours in antibiotic-treated mice	21
	DEN plus CCl4-treated mice, receiving rifaximin	Fewer tumours in rifaximin-treated mice	21
	DEN-treated rats, receiving neomycin	Fewer tumours in neomycin-treated rats	35
	DMBA and high-fat-diet-treated mice, receiving antibiotic cocktail	Fewer tumours in antibiotic-treated mice	22
	DMBA and high-fat-diet-treated mice, receiving vancomycin	Fewer tumours in vancomycin-treated mice	22
Lung cancer	NHMI-treated germ-free rats	Fewer tumours in male germ-free rats No change in female germ-free rats	24
Breast cancer	DMAB-treated germ-free rats	Reduced tumours in germ-free rats	26
Human studies
Gastric cancer	H. pylori eradication by antibiotics	Reduced cancer in antibiotic-treated patients	39,40
Gastric MALT lymphoma	H. pylori eradication by antibiotics	Regression after eradication	51
Skin MALT lymphoma	Borrelia burgdorferi eradication by antibiotics	Regression after eradication	53
IPSID	Campylobacter jejuni eradication by antibiotics	Regression after eradication	52
Ocular adnexal lymphoma	Chlamydia psittaci eradication by doxycycline	Regression after eradication	54

AOM, azoxymethane; Apc, adenomatous polyposis coli; CCl₄, carbon tetrachloride; Cdx2, caudal type homeobox 2; DEN, diethylnitrosamine; DMAB, 3,2′-dimethyl- 4-aminobiphenyl hydrochloride; DMH, dimethylhydrazine; DSS, dextran sodium sulphate; Il10, interleukin-10; IPSID, immunoproliferative small intestinal disease; MALT, mucosa-associated lymphoid tissue; MAM-GlcUA, methylazoxymethanol-β-D-glucosiduronic acid; NHMI, N-nitrosoheptamethyleneimine; Nod, nucleotide-binding oligomerization domain-containing.