Merkel cell carcinoma in Western Australia: a population-based study of incidence and survival

Background Merkel cell carcinoma (MCC) is an uncommon but aggressive cutaneous skin cancer. Even with the appropriate treatment, MCC is prone to recurrence, and metastases are common. Exposure to ultraviolet radiation has been suggested as contributing towards the development of MCC. MCC has not been extensively investigated in Australia, even though Australia has the highest incidence of sun-related cancers in the world. Objectives To describe the demographics and determine trends of incidence and survival of MCC cases in Western Australia (WA). Methods All reported invasive cases of MCC incident between 1 January 1993 and 31 December 2007 were extracted from the WA Cancer Registry. Age-adjusted incidence rates for MCC were calculated using direct standardization to the U. S. standard 2000 population. Cause-specific survival was investigated using Kaplan-Meier and Cox proportional hazards analysis. Results Two hundred and fifteen cases were confirmed by pathological review as being definite cases of MCC. Patients were mainly males (65%) and elderly (median age 77 years). Standardized age-adjusted incidence rates were higher in men (1.0/100 000) than in women (0.63/100 000) and higher in older ages (15.5/100 000 in the 85+ year age group) than younger ages (0.1/100 000 in the 30-34 year age group). Five-year cause-specific survival was 64%. Conclusions Incidence of MCC in WA is the highest reported in the literature. In addition, MCC has worse survival than melanoma. The high rates and demographic and anatomical distribution are consistent with sun exposure playing a causal role.