Epidemiology and survival of Merkel cell carcinoma in the Netherlands. A population-based study of 808 cases in 1993-2007.

BACKGROUND: Merkel cell carcinoma (MCC) is a rare and highly malignant neuroendocrine tumour, predominantly located on sun-exposed areas of the skin. The aim of this study was to evaluate data in the Netherlands concerning incidence, stage, age, sex, location, treatment and survival.
METHODS: Using nationwide data from the Netherlands Cancer Registry from 1993 to 2007, we compared 808 MCCs with European data and the US Surveillance, Epidemiology and End Results (SEER) Program.
RESULTS: The annual age standardised incidence rate per million of MCC increased from 1.7 in 1993-1997 to 3.5 in 2003-2007. Median age at diagnosis was 76 years. The most common location was the head and neck. Three quarters of patients had localised disease, 16% regional and 6% distant metastasis. Surgery was performed in 89% of patients, with adjuvant radiotherapy in 26% of them. One-, five- and ten-year relative survival was 85%, 62% and 47%, respectively. Negative predictive factors for the risk of death were male sex, increasing T-stage, regional and distant metastasis and no treatment. Survival after combined surgery and radiotherapy was borderline significantly better than surgery alone (HR 0.82, p=0.09). Our results are comparable to SEER data except for the ratio localised/regional disease. We observed less regional cases (16% versus 31%); while ten-year survival of localised cases was lower (51% versus 71%).
CONCLUSIONS: MCC incidence rates have doubled in the Netherlands over the period 1993-2007. The relatively high number of localised cases and their relatively low survival as compared to SEER data suggest that a substantial proportion is undertreated.