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Acne and Melanoma: What to Do With the Reported Connection?
Dermatologists have become accustomed to reading about the associations of dermatologic disease with extracutaneous comorbidities (psoriasis...
The incidence of cutaneous melanoma (CM) has increased, warranting further study of new risk factors.1,2 Hereditary risk factors for CM include light-colored eyes; fair skin; light brown, blonde, or red hair; tendency to burn; high density of freckles; history of other types of skin cancer; high number of common, atypical, and/or congenital nevi; and family history of skin cancer, as well as risks related to the presence of CDKN2A, BRAF, and MC1R gene mutations. Environmental risk factors include UV exposure from sunlight or tanning beds, among others.3-5
Nutritional factors also have been suggested as possible modifiable risk factors for CM.6 Evidence from epidemiological studies show that diets rich in fruits and vegetables are associated with lower risks for several types of cancer.7,8 A growing number of studies have assessed the effects of diet and the intake of nutrients on the prevention of cancer, specifically the use of dietary supplements to protect the skin from the adverse effects of UV light.6
Preformed vitamin A (ie, retinol) is necessary for the regulation of cell differentiation and also can reduce the incidence of skin tumors in animals exposed to UV light. Certain carotenoids such as α-carotene and β-carotene are metabolized to retinol. These retinol precursors, along with antioxidant nutrients, are important components of fruits and vegetables and may account for the observed anticancer effects of these foods.8
The aim of this study was to assess the relationship between dietary intake and the risk for CM.
Methods
Participants
A case-control study was carried out between 2012 and 2013 at 3 reference centers in Porto Alegre, Brazil—Universidade Federal de Ciências da Saúde de Porto Alegre, Pontifícia Universidade Católica do Rio Grande do Sul, and Hospital de Clínicas de Porto Alegre—for the treatment of patients with CM. Enrolled patients were 18 years and older with a diagnosis of primary CM confirmed by histology. Controls were selected from patients at the same centers, and they were enrolled and matched by institution. Controls were frequency matched to cases by sex and age (+/– 5 years). Exclusion criteria for controls were those presenting with suspicious lesions and those needing radiation therapy or chemotherapy due to other diseases. The study was approved by the ethics committees of the participating centers and informed consent was obtained from all participants. A total of 191 participants (95 cases; 96 controls) were enrolled in the study.
Data Collection
After informed consent was obtained, participants were interviewed and were clinically examined by an experienced dermatologist (C.B.H. and M.M.S.). The questionnaire included sociodemographic variables, medical history, phenotypic characteristics (ie, Fitzpatrick skin type, skin/hair/eye color), family history of skin cancer, history of sunlight exposure, history of sunburns, use of artificial tanning, sunscreen use, and detailed dietary intake. Physical examination included the assessment of several melanocytic lesions (nevi, freckles/ephelides, lentigines, and café au lait spots), actinic keratoses, solar elastosis, and nonmelanocytic tumors following the International Agency for Research on Cancer (IARC) protocol.9
Using a food frequency questionnaire, participants were asked to report their usual frequency of consumption of each food from a list of 36 foods. The frequency of intake of all groups of food and beverages was defined according to the following scale: never, rarely (less than once monthly), once or twice weekly, 3 to 4 times weekly, 5 to 7 times weekly, and more than 7 times weekly. Combination of categories was based on the overall distribution among controls. Therefore, for some items such as mussels and fresh herbs, only 2 categories were used.
Statistical Analysis
A descriptive statistical analysis of the results was performed using SPSS version 20.0 with absolute and relative frequencies for the categorical variables, and mean, SD, and median for the continuous variables. The symmetry of distributions was investigated using the Kolmogorov-Smirnov test.
A t test for independent groups was applied for the continuous variables, while the Pearson χ2 test was used for the categorical variables. The Fisher exact test was used in situations in which at least 25% of the values of the cells presented an expected frequency of less than 5. Monte Carlo simulation was used when at least 1 variable had a polytomic characteristic. Odds ratio (OR) was used to estimate the strength of the association between exposures and outcome. An unconditional binary logistic regression was used to study the association between dietary variables and the risk for CM. To obtain unbiased estimates, multivariate analyses were performed controlling for 1 or more confounding variables. Using low exposure as a base category, the risks and 95% CIs were calculated for the high-exposure categories. Based on the results of bivariate analyses, variables with P≤.25 or lower were included in the models. The likelihood ratio test was used to decide which covariates should be maintained in the model. To test the goodness of fit of the models, the Hosmer-Lemeshow statistic was used.
