Incidence and survival for Merkel cell carcinoma in Queensland, Australia, 1993-2010.

IMPORTANCE: Merkel cell carcinoma (MCC) is an uncommon but highly invasive form of skin cancer. The mechanisms that cause MCC are yet to be fully determined.

OBJECTIVES: To compare the incidence and survival rates of MCC in Queensland, Australia, known to be a high-risk area, with MCC incidence and survival elsewhere in the world. We also analyzed incidence trends and differences in survival by key demographic and clinical characteristics.

DESIGN, SETTING, AND PARTICIPANTS: Retrospective cohort study of population-based administrative data for MCC collected by the Queensland Cancer Registry and supplemented with detailed histopathologic data. Deidentified records were obtained of all Queensland residents diagnosed as having MCC during the period from 1993 to 2010. A subsample of histopathologic records were reviewed by a senior dermatopathologist to determine the potential for misclassification. A total of 879 eligible cases of MCC were included in the study.

MAIN OUTCOMES AND MEASURES: Incidence rates were directly age standardized to the 2000 United States Standard Population. Trends were examined using Joinpoint software with results expressed in terms of the annual percentage change. The period method was used to calculate 5-year relative survival, and adjusted hazard ratios were obtained from multivariate Poisson models.

RESULTS: There were 340 cases of MCC diagnosed in Queensland between 2006 and 2010, corresponding to an incidence rate of 1.6 per 100,000 population. Men (2.5 per 100,000) had higher incidence than women (0.9 per 100,000), and rates peaked at 20.7 per 100,000 for persons 80 years or older. The overall incidence of MCC increased by an average of 2.6% per year from 1993 onwards. Relative survival was 41% after 5 years, with significantly better survival found for those younger than 70 years at diagnosis (56%-60%), those with tumors on the face or ears (51%), and those with stage I lesions (49%).

CONCLUSIONS AND RELEVANCE: Incidence rates for MCC in Queensland are at least double those of any that have been previously published elsewhere in the world. It is likely that Queensland's combination of a predominantly white population, outdoor lifestyle, and exposure to sunlight has played a role in this unwanted result. Interventions are required to increase awareness of MCC among clinicians and the public.