Merkel cell carcinoma: A Forty-year experience at the Peter MacCallum Cancer Centre

Background Merkel cell carcinoma (MCC) is a rare but highly aggressive neuroendocrine skin malignancy, with Australia having the highest reported incidence in the world. There is currently a lack of consensus regarding optimal management approach. Methods This was a retrospective audit conducted by reviewing existing medical records of MCC patients presenting to the Peter MacCallum Cancer Centre (PMCC) between 1980 and 2018. The primary endpoint was locoregional control. The secondary endpoints were distant recurrence, disease-free survival and overall survival. Results: A total of 533 patients were identified. The estimated 5-year OS and DFS were 46% (95% Confidence Interval [CI] 41 - 51%) and 34% (95% CI 30 - 39%) respectively. Older age at diagnosis (hazard ratio [HR] per year 1.07 95% CI 1.06 - 1.09; p<0.001), and larger primary tumour diameter (HR 1.22 95% CI 1.09 – 1.37; p = 0.001) were associated with worse OS on multivariable analysis. Positive or negative histopathological margin status was not associated with OS or DFS in patients treated with post-operative radiotherapy. Conclusions In our study, about a third of patients developed locoregional recurrence and/or distal recurrence, and there appears to be no change over the last four decades. If treated with adjuvant radiotherapy, there is no difference in OS or DFS with positive surgical margins. Findings should influence future guidelines.