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An estimation of the prevalence of nonmelanoma skin cancer in the U.S.

Nonmelanoma skin cancer (NMSC) is the most commonly diagnosed cancer in Australia and has a significant impact on the cost of and use of healthcare resources. Current estimates of NMSC in the USA are 3.5 million cases in 2010 compared to 1.63 million cases of all other cancers combined. However, we believe that this figure significantly underestimates the prevalence of NMSC in the USA. We calculated that melanoma is diagnosed 5.7 times more in the USA than in Australia. In Australia, in 2010, there were 767,000 NMSC diagnoses. If the ratio of melanoma: NMSC is constant in both Australia and the USA, then there should be 5.7 times the number of NMSC in the USA or 4.3 million cases. The assumptions that underlie this calculation are discussed.

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Introduction
Nonmelanoma skin cancer (NMSC) includes basal cell carcinoma and squamous cell carcinoma of the skin, and is common in both Australia and the USA. In fact, in both Australia and the USA, NMSC is more common than all other forms of cancer combined 1-3 . NMSCs are predominately managed privately in an outpatient setting. NMSC is not a reportable cancer and NMSC data are not recorded on national cancer registries in either Australia or the USA.
Estimates of the incidence of NMSC in both Australia and the USA are obtained by periodic surveys. Incidence data record an individual's first episode of skin cancer within a calendar year. As NMSC patients commonly develop multiple primary cancers, incidence data are likely to significantly underestimate the burden of disease.
In order to calculate NMSC prevalence in Australia, data from more than 8 million skin cancers treated between 1 January 1997 and So, what is the prevalence of NMSC in the USA? Rogers et al. estimated that in 2010 more than 3.5 million skin cancers were diagnosed in over 2 million people 2 . The number of practicing dermatologists in USA in 2010 was 9598 7 . This figure suggests on average that each dermatologist treats 364 NMSCs a year, or one a day. Anecdotally, this figure seems low, even accounting for differences of skin cancer prevalence in each state.
Another way to estimate the burden of NMSC in USA is to compare the incidence of melanoma in the USA to that in Australia. Melanoma is a cancer that is reportable in both the USA and Australia.
Reporting is mandatory and data on melanoma prevalence are likely to be more complete compared to data on NMSC.
In 2010, it was predicted that 68,130 melanomas would be recorded on the cancer registry in the USA 3 and 11,900 were predicted for the national cancer registry in Australia in 2010 1 . This amounts to 7.1 melanomas per dermatologist per year in the USA and 21.6 melanomas per dermatologist in Australia in 2010.
National registries data indicate that 5.7 times the number of melanomas were diagnosed in the USA among a population that is 14 times larger than Australia. One model 6 assumes that the climate, ethnicity, sun exposure behaviour and population differences that lead to the higher incidence of melanoma in Australia do not affect the ratio of melanoma to NMSC. We also assume that melanoma is recorded with equal accuracy and completeness in both the USA and Australia. Based on these assumptions, the number of NMSCs treated in the USA in 2010 would also be 5.7 times the number of NMSCs treated in Australia. As 767,000 NMSCs were treated in Australia in 2010, we estimate that 4.3 million NMSC were treated in USA. Author contributions RS conceived the article. EP and RS prepared the first draft of the manuscript. All authors were involved in the revision of the draft manuscript and have agreed to the final content.

Competing interests
No competing interests were disclosed.

Grant information
The author(s) declared that no grants were involved in supporting this work. 1.