June 21, 2012 — Smoking cigarettes and using other forms of tobacco significantly increase the risk for cutaneous squamous cell carcinoma (SCC), according to the first-ever systematic review of the literature.
However, smoking does not increase the risk for basal cell carcinoma (BCC), report the authors of the review, led by Jo Leonardi-Bee, PhD, from the University of Nottingham in the United Kingdom.
The study was published online June 18 in the Archives of Dermatology.
Together, SCCs and BCCs comprise about 97% of all skin cancers.
Although evidence has demonstrated that smoking is a risk factor for oral SCC, it has been unclear whether smoking modifies the risk for these skin cancers.
After reviewing 25 studies (either cohort or case-control design), Dr. Leonardi-Bee and her colleagues found that smoking is "significantly associated" with cutaneous SCC (pooled odds ratio, 1.52; 95% confidence interval, 1.15 to 2.01).
It is important for clinicians to actively survey current smokers to identify early skin cancers.
"It is important for clinicians to actively survey current smokers to identify early skin cancers," they advise.
The quality of the new evidence is an A, which means that it applies to "most patients" of relevance, and is grade 1, which means that it is a "strong recommendation."
The largest effect sizes for an association with cutaneous SCC were seen in current and in ever smokers; smaller effect sizes were seen in former smokers. The study looked at all forms of tobacco exposure, including cigarettes, cigars, chewing tobacco, and "roll-ups" (hand-rolled cigarettes).
The study effectively adds smoking to the list of risk factors for cutaneous SCC. The risk factors for nonmelanoma skin cancers in general include, most prominently, age, skin type, and exposure to ultraviolet (UV) radiation (from sunlight and sunbeds). Other risk factors are precursor lesions (actinic keratosis and Bowen's disease), previous skin cancers, transplanted organs, immunosuppression, exposure to arsenic, treatment with psoralen UV, and albinism.
It is not surprising that only cutaneous SCCs — and not BCCs — are linked to smoking, the authors note.
Nonmelanoma skin cancers are heterogeneous, with varying causes and prognoses, they say. "For example, BCC is slow growing and locally invasive, in contrast to cutaneous SCC, which is generally more aggressive and has the potential to metastasize. Therefore, it would be expected that the effect of smoking on the risk of the diseases would also vary considerably between the subtypes of nonmelanoma skin cancer."
Effect Could Be Even Larger
The authors believe the findings are generalizable because the studies are from 11 countries on 4 continents. Of the 25 studies, 15 are from Australia, North America, and the United Kingdom. Most were conducted in middle-aged to elderly populations.
One of the limitations of this systematic review is that the reporting of smoking was done, in most cases, through either a self-administered questionnaire or a structured interview. Underreporting is likely in such circumstances, say the authors. Thus, "the magnitude of effect could be larger than we have shown," they write.
How smoking causes cutaneous SCC is not known, but the authors offer some thoughts. The possible mechanisms could be related to either reduced immune function or the carcinogenic properties of tobacco, they say.
They include the usual caveat about their type of study — epidemiologic studies cannot prove causation, they can only identify associations.
Arch Dermatol. Published online June 18, 2012. Abstract
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