Outcomes of merkel cell carcinoma: A 10-year population-based study in Queensland, Australia.

e21593 Background: Queensland (QLD) has the highest incidence of Merkel Cell Carcinoma (MCC) within Australia, with a rate of 2.3/100,000 in 2021. This study aims to characterize the epidemiology of MCC in QLD over 10 years between 2012 and 2021 and examine trends in diagnosis, treatment, recurrence, and survival. Methods: A retrospective population-based analysis was conducted using data from the QLD Oncology Repository (QOR). Clinico-pathological information was collected for all MCC cases diagnosed in QLD between 2012 and 2021, with follow-up through to Dec 31, 2023. Kaplan-Meier survival analysis was used to assess overall survival (OS) and recurrence rates. Results: Of 1061 patients diagnosed with MCC, 68% were male, 1% were First Nations, with median age at diagnosis of 78 years (range 26-105). The 5-year OS and MCC-specific survival (MSS) was 42% and 65% respectively. At diagnosis, 63% had stage I/II MCC, 25% stage III, 5% stage IV and 7% unknown. The 5-year overall survival (OS) by primary site was: upper limb 49%, head and neck 45%, trunk 44%, and lower limb 32%. The 5-year recurrence rate was 44%. Among those who experienced a recurrence, the median time to recurrence was 11 months, with 80% occurring within 2 years and 94% within 3 years. Immunosuppressed patients (27% of the cohort) had worse survival compared to non-immunosuppressed patients, with 5-year OS of 32% vs 46%, and 5-year MSS of 59% vs 67% respectively. Other independent predictors of increased mortality included age, advanced stage, and high comorbidity burden (p < 0.001). Metastatic disease (excluding nodal) occurred in 23% of the cohort, with liver metastasis in 16% and brain metastasis in 6%. Patients with liver and brain metastases had worse outcomes, with 5-year OS of 13% and 15%, respectively, compared to 36% for other metastatic sites. 64% of patients in the entire cohort received radiation therapy, and 26% received systemic therapy. Among stage III/IV patients, those treated with avelumab (n = 101) had a higher 5-year MSS compared to those not treated (n = 466): 54% vs 46%. The rate of avelumab use increased > 5 fold from the 5 year period (2012-16) to (2017-21). Over the same period, 5 year OS also improved from 61% (2012-16) to 69% (2017-21), despite an ageing population (44% patients aged > 80 in 2012-16, compared to 47% aged > 80 in 2017-21). Conclusions: MCC incidence in QLD is among the highest globally and has steadily increased since 1982. Majority (94%) of recurrences occurred within the first 3 years. Independent predictors of poor OS include age, advanced stage, and comorbidity burden, with immunosuppression predictive of poorer OS and MSS. Patients with lower limb primary disease had the worst outcomes; and within stage IV disease, those with liver or brain metastases have worse outcomes. Despite an increasing aging population, OS and MSS have improved over time, which may be linked with increased use of immunotherapy.