Epidemiology and survival of Merkel cell carcinoma in New Zealand: A population-based study between 2000 and 2015 with international comparison

Background/objectives Merkel cell carcinoma is an aggressive neuroendocrine skin cancer. Australian studies report high incidence and poor survival rates compared internationally. While New Zealand has a comparable UV index and racial composition to Australia, survival outcomes are currently unknown. The role of Merkel cell polyoma virus in oncogenesis of Merkel cell carcinoma is an active area of research. We describe the incidence and survival of Merkel cell carcinoma in New Zealand with correlation to demographic and clinical factors including regional polyoma virus prevalence. Methods Retrospective study of population-based data from the New Zealand Cancer Registry. Incidence rates were directly standardised to the US standard 2000 population. Survival was investigated using Kaplan-Meier and multivariable Cox regression models. Results Six hundred and one cases were diagnosed in New Zealand between 2000 and 2015. The overall incidence rate was 0.96/100 000 population. Merkel cell carcinoma is more common in males, elderly and on sun-exposed areas. Eighteen percent of patients were diagnosed with distant metastasis at time of presentation. The overall 5-year survival rate and relative 5-year survival rate were 31% and 45%, respectively. Mortality was 1.9 and 2.5 times higher for stage III and IV disease, respectively, relative to stage I/II disease. Patients over age 80 had twice the mortality compared to those aged 60-69. Conclusions New Zealand has a high incidence of Merkel cell carcinoma and poor survival outcomes when compared internationally. We have the highest proportion of distant metastatic disease at time of diagnosis. Further research into the role of nonpolyoma-related Merkel cell carcinoma is warranted to improve Merkel cell carcinoma outcomes in New Zealand and abroad.