Could alcohol consumption increase the risk of melanoma and non-melanoma skin cancer?

Could alcohol consumption increase the risk of melanoma and non-melanoma skin cancer?

A recent report from more than 59,000 women in the Women’s Health Initiative related alcohol consumption to the risk of melanoma (MM) and non-melanoma skin cancer (NMSC). This was a fairly large study, with 532 cases of melanoma and 9,593 cases of NMSC occurring over around ten years of follow up.

The key reported results were for a higher hazard of MM (HR 1.64) and NMSC (OR 1.23) for drinkers of seven or more drinks per week, compared with non-drinkers. Lifetime alcohol consumption was also positively associated with the hazard of MM and risk of NMSC, with the only significant increases for MM according to type of beverage seen for women with a preference for white wine or liquor. As shown in many previous studies, the risk of these skin cancers was lower among smokers than among non-smokers.

Forum reviewers thought that this was a very well-done analysis. They did note that there were large decreases in the estimates of HRs related to alcohol consumption when adjustments were made for sun exposure and other known confounders. For example, the HR for MM decreased for total wine from 1.30 to 1.06 when adjusted; for red wine, from 1.71 to 1.34; for white wine, from 1.93 to 1.52; for liquor, from 1.87 to 1.65; and for beer, from 1.34 to 1.18.

The magnitude of these changes, as well as the very different baseline characteristics of the women according to their drinking habits, raises the possibility that there may be residual confounding affecting the results. In addition, one reviewer points out that, by including subjects with these skin cancers prior to baseline in their main analyses, there could be a problem with bias in their results.

Forum member Klatsky has recently reported on this topic using several decades of follow-up data from the Kaiser-Permanente study, with more than 300,000 subjects and more than 1,000 cases of MM. In that study, he and his colleagues found that, among persons preferring wine, the HR for MM at 3+ drinks per day was 1.7 (1.2-2.5), while it was 1.2, 1.3, and 1.1 in persons with preference for liquor, beer, and no beverage type, respectively.

However, at 1-2 drinks per day, wine drinkers had a HR of 0.9. Klatsky states “Maybe too much should not be made of the beverage type data in these analyses. However, the association with alcohol seems statistically solid.” 

A previous study by Mukamal, with data from 300,000 subjects reporting in a risk factor surveillance survey, reports: “Approximately 33.5% of respondents reported a sunburn within the past year. Heavier average alcohol use and binge drinking were both positively associated with prevalence and number of sunburns within the past year.

"The adjusted odds ratios for prevalence and number of sunburns among binge drinkers were 1.39 (95% confidence interval 1.31-1.48) and 1.29 (95% confidence interval, 1.20-1.38), respectively.”

Klatsky wonders whether “possible confounding by sun is not only an artefact of SES and tropical vacations, but whether heavy imbibers at the beach may fall asleep when exposed or simply do not notice their sunburn until it is severe.” Other forum reviewers also worry that there may be residual confounding in the present study from sun and ultraviolet exposure.

Klatsky adds: “Even if the alcohol-melanoma association is due to confounding by sun exposure, the same explanation seems less plausible for the inverse association between smoking and melanoma. While there is obviously no public health utility in any ‘protective’ effects of smoking, that association is scientifically interesting and could be a clue to mechanisms.”

The bottom line is that there are considerable observational epidemiologic data suggesting that alcohol consumption may relate to an increase in the risk of MM and NMSCs. As mechanisms are not known, there is still concern that much of this relation may relate to residual confounding by ultraviolet sun exposure, the most important environmental factor for these diseases.

To read the full critique, click here.

These critiques are published with the permission of The ISFAR.