Merkel Cell Carcinoma in Queensland: Treatment, Incidence and Outcomes Over a 10-Year Period (2012-2021)

Merkel Cell Carcinoma (MCC) is a rare skin cancer with aggressive behaviour. We present results for incidence and outcomes of MCC in Queensland, a population having the highest rates of skin cancer worldwide.

Data for patients diagnosed with MCC between 2012 and 2021 were obtained from the population-based Queensland Oncology Repository. The age-standardised incidence rate trend was assessed using Joinpoint regression. Five-year MCC-specific survival was estimated using the Kaplan-Meier method and factors independently associated with survival were determined from a Fine-Grey multivariable model.

A total of 1061 patients with MCC were included. Median age at diagnosis was 78 years, 68% were male and 27% were immunocompromised. Nearly all patients (94%) received treatment within 365 days of diagnosis, of whom 79% had surgery, 58% had radiotherapy and 15% had intravenous systemic therapy, either alone or in combination with other modalities. The average annual incidence rate was 1.89 per 100,000 population and remained stable over the study period (p_trend = 0.13). Over one-third (35%) of the study cohort developed recurrences within 5 years, with a median time to recurrence of 11 months. Five-year MCC-specific survival increased from 61% between 2012 and 2016 to 69% during 2017-2021 (p = 0.01). Older age at diagnosis, higher tumour stage, a greater number of co-morbidities and immunosuppression were significantly associated with poorer survival.

Our results indicate that the incidence of MCC in Queensland has stabilised following a long period of rapid increases. MCC-specific survival is improving, mostly for more advanced tumours, which is likely attributable to increasing use of immunotherapy.