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

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 31 December 2010⁴ were evaluated by Fransen et al. Data from the study were obtained from Medicare Australia. The population of Australia grew 23% from 18.3 million in 1997 to 22.6 million in 2010⁵. Roughly 95% of the population or 21,470000 people are of European or Anglo-Saxon descent. Medicare Australia is a Commonwealth Government-funded universal health insurance scheme. Medicare Australia data captures 98% of all skin cancer treatments in Australia. Fewer than 2% of NMSC lesions are treated in public hospitals that record data independently⁶. All skin cancer treatments in Australia, except those provided in a public hospital, are individually itemized and recorded by Medicare Australia for the purpose of patient reimbursement. Item numbers for the excision, cryotherapy, curettage or laser treatment of skin cancers require histological confirmation of the diagnosis or clinical diagnosis by a registered dermatologist prior to Medicare coding.

The total number of NMSC treatments increased by 186% from 412,493 in 1997 to 767,347 in 2010⁴. The number of treatments are estimated to increase to 938,991 (95% CI, 901,047–976,934) by 2015⁴.

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 people². The number of practicing dermatologists in USA in 2010 was 9598⁷. 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 USA³ and 11,900 were predicted for the national cancer registry in Australia in 2010¹. 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 model⁶ 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.

The population of the USA was 308.7 million in 2010 and 72.4% were White or European American⁸, 12.6% were black or African American⁸. The remaining 15% comprised people of different ethnicities including Hispanic or Latino, Asian, Native American, Hawaiian and Pacific Islanders⁸. The skin cancer with the least ethnic variation in incidence is acral lentiginous melanoma (ALM). ALM only represents 2–3% of all melanoma diagnosed in the USA⁹. If ALM were excluded from the total number of melanomas diagnosed in the USA in 2010, that reduces our estimate of NMSC in USA from 4.3 to 4.21 million cases.

This is roughly an extra 700,000 cases on top of the current estimations of NMSC by Rogers et al². This now equates to approximately 1.2 NMSCs per US dermatologist per day. Anecdotal experience would suggest this figure still underestimates the true burden of NMSC in USA. A prospective registry may be required to better estimate the full burden of NMSC and to ensure that there are adequate physical resources and manpower to treat NMSC patients in the USA.