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.