Understanding the molecular mechanisms of cancer prevention by dietary phytochemicals: From experimental models to clinical trials

Table 1 Successful cancer prevention approaches

Cancer prevention approach	Measures undertaken	Demonstration in epidemiological studies/clinical trials	Ref.
Avoid/minimize exposure to known carcinogens/risk factors	Quit cigarettes smoking	Epidemiological study followed up for 40 yr on male British doctors demonstrated decrease in risk	[39-41]
	Decreasing proportion of young smokers	Decrease in mortality due to lung cancer among younger male cohort
	Reduction in number of cigarettes/day or duration of smoking and time since stopping smoking	Epidemiological study - decrease in the rate of lung cancer	[42]
	Ban the production and reduce the usage of carcinogenic aromatic amines	Reduction in bladder cancer among the dye workers	[43]
	Improvement in food preservation techniques	Significant reduction in incidence and mortality due to gastric cancers	[44]
Vaccination	HPV vaccines	Have shown 95%-100% effectiveness in preventing the cervical cancer precursor lesions and in preventing cervical adenocarcinoma in situ. Protection conferred was highly variable in those with prior HPV infection	[45-47]
	Gardasil (HPV 6,11,16,18)
	Cervarix (HPV 16,18)
	HBV vaccines	Rate of HCC decreased in children (6-14 yr)	[48]
	Engerix-B (HBV-DNA)
	Recombivax (HBV surface antigen)
Surgical intervention	Prophylactic resection of high risk organs-bilateral mastectomy and oophorectomy in BRCA1/BRCA2 mutations carriers	Decrease in breast cancer risk and breast and ovarian cancer risk	[49-51]
	Colostomy in FAP patients	Decrease in colorectal cancer risk in patients with APC mutations	[52,53]
Chemoprevention
Non melanoma skin cancer	Topical application of 5-FU, Immiquimod, Diclofenac, PDT with delta-aminolevulinic acid, Ingenolmebutate	Partial or complete clearance of actinic keratosis leading to decrease in cancer	[54-64]
Skin melanoma	Daily or discretionary sunscreen (SPF15+) for 4 yr	Reduction in invasive melanoma in a community based trial	[22]
Breast cancer	Administration of selective estrogen receptor modulating agent(s) (Tamoxifen, Reloxifen)/aromatase inhibitors (Exemestane)	Trials have demonstrated efficacy of these agents in breast cancer prevention, reduction in recurrence and mortality	[25,65,66]
Prostate cancer	Administration of androgen receptor blockers (Finasteride, Dutasteride)	Reduction in prevalence and risk in clinical trials	[67-70]
Colorectal polyps, Adenomas, and cancer	Administration of NSAIDs- Aspirin, Celecoxib, Rofecoxib, Sulindac, DFMO	NSAIDs-mediated reduction in colorectal adenomas	[24,27,51,71-75]
		Significant increase in time to first colorectal cancer occurrence

HPV: Human papillomavirus; HBV: Hepatitis B virus; HCC: Hepatocellular carcinoma; BRCA: Breast cancer; 5-FU: 5-Fluorouracil; PDT: Photodynamic therapy; NSAIDs: Non-steroidal anti-inflammatory drugs; APC: Adenomatous polyposis coli; DFMO: Difluoromethylornithine.