Merkel cell carcinoma incidence is increasing in Sweden.

BACKGROUND: Merkel cell carcinoma (MCC) is a rare aggressive neuroectodermal skin cancer with a high recurrence rate and a high mortality rate. Risk factors for MCC are reported to include high age, UV exposure, Caucasian skin type and immunosuppression. The incidence is reported to be increasing.

OBJECTIVE: The purpose of this study was to describe a Swedish cohort and calculate incidence.

METHODS: The study design is a retrospective cohort study of population-based data for MCC collected by the Swedish Cancer Registry to determine the incidence of MCC in Sweden and the clinical characteristics of these tumours including demographics, TNM classification, body part distribution and overall survival after diagnosis. De-identified data were collected from 1993 to 2012.

RESULTS: A total of 606 cases of MCC were identified during the study period. The median age was 81 years (range 21-99) and a majority, 54.4% were women but age-adjusted incidence is higher in men. The incidence (per 100,000) of MCC in Sweden in 1993-2012 increased from 0.09 to 0.20 for men and 0.12-0.17 for women, adjusted for age to the world standard population. For the both sexes, the increase was from 0.11 to 0.19 per 100 000, an increase of 73%. The most common site of the primary tumour was the head and neck, with 51.8% of the cases. The size of the tumour was <5 cm in 82.1% of the cases. The majority of the tumours (90.7%) had no known lymphatic spread and only a few patients had confirmed distant metastases (2.9%) when diagnosed.

CONCLUSIONS: MCC is a rare disease in Sweden, but the incidence is increasing. This study supports the finding that high age, male sex and UV exposure are risk factors for MCCs. Interventions are required to increase awareness of MCC among clinicians and the public.