A Cochrane review [Abstract] 1 included 10 studies with a total of 7 229 subjects. One trial found that T4N5 liposome lotion significantly reduced the rate of appearance of new basal cell carcinomas (BCCs) in people with xeroderma pigmentosum. One of three trials of renal transplant recipients showed a significantly reduced risk of new non-melanoma skin cancers (NMSCs) when acitretin was compared to placebo (RR 0.22 95% CI 0.06 to 0.90) and no significant difference in risk of adverse events in two trials (RR 1.80, 95% CI 0.70 to 4.61). In three trials conducted in people with a history of NMSC, the evidence was inconclusive for the development of BCCs for retinol or isoretinoin. However the risk of a new squamous cell carcinomas (SCCs) in one trial (HR 1.79, 95% CI 1.16 to 2.76) and adverse events in another trial (RR 1.76 95% CI 1.57 to 1.97) were significantly increased in the isotretinoin group. In one trial selenium showed a reduced risk of other types of cancer compared with placebo (RR 0.65, 95% CI 0.50 to 0.85) but also a significantly elevated risk of a new NMSC (HR 1.17 95% CI 1.02 to 1.34). The evidence for one trial of beta-carotene was inconclusive; and there was a trend towards fewer new NMSC in a trial of a reduced fat diet (RR 0.16, 95% CI 0.02 to 1.31), p=0.09.
Comment: The quality of evidence is downgraded by imprecise results (few patients and wide confidence intervals), by study quality (inadequate or unclear allocation concealment) and by by inconsistency (heterogeneity in interventions and outcomes).
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