Lifestyle factors of smoking, BMI and alcohol on the risk of Non‐Melanoma Skin Cancer in adults: a systematic review

Background Non‐melanoma skin cancer is the most common cancer in humans and the most important risk factors are thought to be age, skin type, and exposure to ultraviolet radiation. Lifestyle factors may also play a part. To date no systematic review has been performed to collate evidence of the effects of smoking, alcohol or body mass index. Objectives We performed a systematic review and meta‐analysis to assess the effects of smoking, alcohol and body mass index on the risk of non‐melanoma skin cancer and its subtypes. Inclusion criteria Types of participants Adults (18+ years old) of either sex from any ethnicity Types of exposures Smoking, alcohol, or body mass index (including other anthropometric measurements, such as weight, waist to hip ratio, and the percentage body fat) Types of outcomes Non‐melanoma skin cancer, cutaneous squamous cell carcinoma, or basal cell carcinoma Types of studies Comparative observational epidemiological studies Search strategy We performed a comprehensive search of MEDLINE, EMBASE, CINAHL, Cochrane Library and CAB Abstracts from inception to October 2010. We also scanned reference lists to identify further eligible studies. Methodological quality Data from eligible studies were extracted and quality assessed using the Newcastle Ottawa Scale independently by two reviewers. Data collection The titles, abstracts and full text identified from the search were assessed independently by two reviewers against pre‐specified inclusion/exclusion criteria. Disagreements were resolved through discussion with a third reviewer. Data synthesis For studies with similar exposures, a meta‐analysis was performed using a random effects model and results were expressed as pooled odds ratio with 95% confidence intervals. Heterogeneity was assessed using I2. Publication bias was assessed using funnel plots. Data were analysed using Review Manager. Results Thirty studies were included of which 22 used a case control design and the remaining used a cohort design. The overall quality of the studies was variable with a Newcastle Ottawa Scale median score of 6 out of 9 stars. No evidence of asymmetry was detected in the funnel plots. Smoking was not significantly related to increased risks of non‐melanoma skin cancer (Odds Ratio 0.62, 95% CI 0.21 to 1.79, I2=34%, 2 studies) or basal cell carcinoma (Odds Ratio 0.95, 95% CI 0.82 to 1.09; I2=59%, 14 studies). However, smoking was significantly associated with a 52% increase in the risk of cutaneous squamous cell carcinoma (95% CI 1.15 to 2.01; I2=64%; 6 studies). Subgroup analysis found no significant difference in results based on the definition of smoking (current, former, or ever smoker) for basal cell carcinoma, cutaneous squamous cell carcinoma or non‐melanoma skin cancer. Alcohol was not significantly related to increased risks of non‐melanoma skin cancer (1 study), basal cell carcinoma (Odds Ratio 1.03, 95% CI 0.94 to 1.13, I2=0%, 9 studies) or cutaneous squamous cell carcinoma (1 study). Similar results were found irrespective of the type of alcohol assessed (beer, wine, or spirits) for basal cell carcinoma and cutaneous squamous cell carcinoma. A pooled analysis of five studies found a non‐significant decrease in the risk of basal cell carcinoma associated with a higher body mass index (Odds Ratio 0.94, 95% CI 0.84 to 1.04, I2=40%). In a subgroup analysis based on sex, the potential reduction in risk of basal cell carcinoma appeared to be confined to males (Males: Odds Ratio 0.90, 95% CI 0.78 to 1.04, I2=45%, 4 studies; Females: Odds Ratio 1.01, 95% CI 0.85 to 1.19, I2=14%, 3 studies). Conclusion It is unclear at present if smoking modifies the risk of basal cell carcinoma; however, smoking clearly increases the risk of cutaneous squamous cell carcinoma. Limited evidence has been published about the risk of non‐melanoma skin cancer with alcohol and body mass index; however there is some suggestion a high body mass index may be slightly protective of basal cell carcinoma, particularly in males. Implications for Practice This study highlights the importance for clinicians to actively survey high risk patients, including current smokers. Implications for Research The majority of studies included in this systematic review assessed the associations between basal cell carcinoma and smoking, alcohol or body mass index. However, more evidence is needed before conclusive recommendations can be formed regarding the relationship between cutaneous squamous cell carcinoma and alcohol or body mass index.