Increased Melanoma After Regular Sunscreen Use?
Authors: Michael A. Goldenhersh, Meni Koslowsky
Journal: Journal of Clinical Oncology (2011)

The article by Green et al 1 is being summarized in medical news reviews on the Internet as proof that use of sunscreen reduces melanoma risk.We believe that such a farreaching conclusion is not justified.Although the longitudinal design and detailed data collection reported by the authors demonstrates inordinate effort, diligence, and perseverance, there seem to be serious limitations in the study that do not allow definitive conclusions to be drawn.To convincingly show a cause-effect relationship, the ideal study should be truly prospective and double blinded. 2,3This investigation was indeed designed to be prospective but only for the examination of nonmelanoma skin cancer.With respect to melanoma, the research seems to be more retrospective than prospective.In support of this contention is the fact that the original study design excluded trunk and lower extremities, the sites where melanomas most commonly occur.In addition, although the authors provide a legitimate ethical reason for not applying a placebo to the control group, it still weakens the experimental nature of the study and eliminates an important feature of an ideal experimen: the double-blinded characteristic.With respect to the main finding of a reduction in the occurrence of primary melanoma, the authors themselves state that "the result was of borderline statistical significance."1p260 Regarding a secondary finding of a 73% reduction in invasive melanoma, the authors state, "This result for the invasive subgroup was an exploratory finding, however, and should be interpreted cautiously."1p261 From these findings and results it is not clear how the authors concluded that "our findings provide reassurance in view of the widespread uncertainty to date about sunscreen's ability to prevent melanoma."1p262 Moreover, the authors chose to exclude from the statistical analysis the melanomas that were diagnosed in the first year of intervention "because their development was unlikely to have been affected by the introduced sunscreen treatment."1p259 To exclude only the first year was an arbitrary decision.It is noteworthy that in the first 4 years of the study, during which the sunscreen intervention occurred, only one melanoma occurred in the intervention group, whereas six occurred in the control group.This ratio of 6:1 is disproportionate to the ratio during other similar intervals throughout the study.It is highly unlikely that this dramatic difference that occurred shortly after the onset of the study is explained by the sunscreen intervention.If the initial 4 years of intervention were excluded from the statistical analysis, no significant reduction would be found in the occurrence of melanoma in the sunscreen treatment group (P Ͼ .22).Also, using 2 tests, subgroup analyses showed that several other possible comparisons between the intervention and control groups were not significant, including removal of the first 2 years from the analysis (P Ͼ .14),comparing only for back and leg melanomas (P Ͼ .24),or removing all back and leg melanomas (P Ͼ .07).