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Critique 187: Alcohol and squamous cell carcinoma of the skin — 14 June 2016

Skin cancers, whether melanoma, basal cell, or squamous cell, are all increased by ultra-violet rays of the sun, and such cancers are much more common in areas of the world with more sun exposure. Further, the risk of such cancers is higher among individuals reporting excessive tanning (either from the sun or from tanning salons). The present study was undertaken to judge the relation between alcohol consumption and the risk of cutaneous squamous cell carcinoma (cSCC), an association that is unclear from earlier research. Determining the relation between alcohol and skin cancer is made difficult by the fact that excessive sun exposure has been shown to be greater among consumers of alcohol than among abstainers, thus the potential for confounding.

In the present analyses, combined data from three cohorts of subjects in the US, who had repeated assessments of alcohol intake over many years, were evaluated tor the relation of alcohol to the development of verified cSCC. Subjects included women in two cohorts of the Nurses’ Health Study and men in the Health Professionals’ Follow-up Study. Among subjects providing a total of more than 4 million person-years of follow up, 2,938 cases of cSCC were identified.

The results varied somewhat among the different cohorts, but in the meta-analysis of the three studies using continuous measures of alcohol, there was an increase in risk of cSCC with alcohol intake. Among women, there was a steep increase in risk of cancer for low levels of intake (up to 5 grams of alcohol/day, slightly less than ½ of a typical drink), then a gradual increase in risk thereafter, whereas among men there was more of a gradual increase in risk with larger reported alcohol intake.

Overall, the authors report an increase in risk per typical drink per day of 22% for invasive cSCC and 14% for in situ cSCC. In beverage-specific analyses, white wine consumption of >/= 5 times/week was associated with an increased risk of cSCC (RR 1.31, 95% confidence interval: 1.09-1.59), but an increased risk of cSCC was not seen for other alcoholic beverages. The population-attributable risk associated with alcohol intake of ≥ 20 grams/day (about 1 ½ typical drinks) was 3% of cSCCs.

Forum members considered that the analyses were well done, and the results of the study are consistent with increases in risk associated with alcohol consumption for other types of skin cancer. Given that sun exposure is by far the primary risk factor for skin cancer, and consumers of alcohol tend to have greater number of sunburns (also shown in this study), it is always difficult to determine if residual confounding by sun exposure is playing a role. The authors of this paper attempted to adjust for sun exposure by including in their analyses the typical exposure values in the area of the world where the subjects resided, by recording the frequency that subjects reported 5 or more severe sunburns, and several other measures. As expected, there were reductions in the estimated RR for invasive cSCC when going from age-adjusted RR (1.34) to multivariable-adjusted estimates (1.22) of risk. However, the magnitude of decrease in risk estimates when only those adjustments for sun-exposure were added to the equation cannot be determined from the data presented.

Forum reviewers consider that these analyses support results from many previous studies and indicate that consumers of alcohol have a greater risk than non-drinkers of all types of skin cancer. Attempts to judge how much of this association may be due to residual confounding related to sun exposure are less than conclusive. Various hypotheses have been raised for possible interactions between sun exposure and alcohol, but currently there are no experimental data to test these theories. While the authors conclude that “physicians may consider counseling their patients about the association between alcohol consumption and risk for cSCC,” it might be more advantageous for physicians to focus more on the much greater protection against this disease that would occur if they were able to limit their patient’s exposure to ultra-violet radiation. Reference: Siiskonen S, Han J, Li T, Cho E, Nijsten T, Qureshi A, Alcohol intake is associated with increased risk of squamous cell carcinoma of the skin: three US prospective cohort studies. Nutrition and Cancer 2016;68:545-553.

For the full critique of this paper by members of the International Scientific Forum on Alcohol Research, please click here
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