Discussion
To the best of our knowledge, this research represents the largest skin cancer screening study conducted by a clinician in Australian surfers and swimmers to date. It is also the largest whole-body screening of surfers for skin cancer. Surfers had higher standardized rates (per 100,000) of AK, BCC, SCC and MSC as compared to swimmers, whilst swimmers had a higher standardized rate of SCC in situ. Both aquatic groups (individually and combined) had rates higher than the Australian general population for NMSC and MSC.8,9
The point prevalence rate of PSC (surfers 37.1%, swimmers 21.8%) is within the estimated percent of the Australian general population for surfers (37-55%) 21; however, swimmers were below this rate. It should be noted that these pre-cancerous AK lesions are well recognized as being precursors to the development of BCCs and SCCs21. Therefore, it is reasonable that participants identified with AKs will likely develop BCC and/or SCC sometime in the foreseeable future. Dodds et al22 reported the progress of AK to SCC was approximately one to 10 percent over 10 years.
The standardised rates (per 100,000) of BCC, SCC and MSC were consistently higher than the standardized rates (BCC surfers 27,568, swimmers 18,181 versus 11.8; SCC surfers 9,482, swimmers 7,272 versus 1,035; melanoma surfers 5,172, swimmers 1,818 versus 53.5) previously reported in the Australian general population. The rates reported are similar than rates (per 100,000) previously reported in Australian surfers surveyed by Climstein et al. (BCC 9,124; SCC 2,670; melanoma 1,854).12
Iannacone and colleagues23 previously investigated MSC in Australian adolescents and young adults based upon de-identified data from the Queensland Cancer Registry. They reported an annual incidence of 10.1 per 100,000 for invasive melanoma. Our equivalent MSC rate was 180 to 512-fold comparatively. Unfortunately, the study by Iannacone and colleagues23 focused upon tumour type and did not contain exposure metrics related to UVR. Climstein and colleagues12investigated Australian surfers via a survey as opposed to clinical screenings. They reported a rate of 1,854 per 100,000, which is near identical to the rate found in this study in swimmers (1,818); however, it is below the rate we identified in surfers (5,172). Although Climstein et al.,12 did not report experience, the surfers in this current study were approximately 20% older, with the exposure (hours surfing per year) similar to that reported in the current study (mean 305 vs 330 hrs/yr). The actual skin cancer rate is most likely under reported in the survey study12 as it relied upon participants self-reporting as opposed to the objective methods used in the current study. It is feasible the higher rate of MSC found in the surfers in the present study is attributed to a greater exposure over the lifetime and the methodology of clinical screening as opposed to a survey.
Moehrl and colleagues24previously reported that beach and water sports (and sunburn) are independent risk factors for the development of BCC; it is reasonable that surfing and swimming were therefore, an independent risk factor for the increased rates seen in NMSCs and MSCs. Both groups reported a similar history of sunburns (surfers 62.1%, swimmers 61.8%); however, swimmers reported a significantly (P =.03) higher number of sunburns (n=446) as compared to surfers (n=353). Regrettably, we did not inquire into the severity nor duration of the sunburns in participants. Additionally, AK, BCC and SCC have been shown to be associated with an increased risk (4.3-fold) of developing a MSC25, thereby increasing risk of MSC in our participants who when screened were clear of MSC.
Solar UVR exposure and resultant skin cancers are dependent upon a number of geographical, behavioural and genetic susceptibility factors. Ultra-violet radiation has been estimated to cause approximately 95% of MSCs in areas of high exposure.26 Despite the high usage of chemical and/or physical protection strategies, our participants had a high point prevalence of NMSC and MSCs, suggestive of the long-term detrimental effects of UVR exposure whilst surfing or swimming. Furthermore, there is a direct correlation between sun exposure and UVR exposure, which accounts for 95% of skin cancer cases. This risk is maintained in those participants continuing to surf or swim, which is highly likely as no participants commented upon ceasing their aquatic activity based upon a positive skin cancer screening.
It is well recognized that Fitzpatric skin types 1 and 2 are at highest risk of developing skin cancer due to the reduced pigmentation, as pigmentation affords a natural protection from UVR exposure however, we found the greatest prevalence of skin cancer was in type 4 followed by type 3. Despite the widespread use of Fitzpatrick skin typing, it has been rarely applied in similar research. For example Climstein and colleagues12 assessed skin type however, simplified the Fitzpatrick skin type to only fair to black, contrary to its intended clinical application. Other related studies neglected to investigate Fitzpatrick skin type altogether27-30therefore limiting comparisons to our findings.