Pre-operative ctDNA predicts survival in high-risk stage III cutaneous melanoma patients

Background: The outcomes of patients with stage III cutaneous melanoma who undergo complete surgical resection can be highly variable, and estimation of individual risk of disease recurrence and mortality remains imprecise. With recent demonstrations of effective adjuvant targeted and immune checkpoint inhibitor therapy, more precise stratification of patients for costly and potentially toxic adjuvant therapy is needed. We report the utility of pre-operative circulating tumour DNA (ctDNA) in patients with high-risk stage III melanoma. Patients and methods: ctDNA was analysed in blood specimens that were collected pre-operatively from 174 patients with stage III melanoma undergoing complete lymph node (LN) dissection. Cox regression analyses were used to evaluate the prognostic significance of ctDNA for distant metastasis recurrence-free survival and melanoma-specific survival (MSS). Results: The detection of ctDNA in the discovery and validation cohort was 34% and 33%, respectively, and was associated with larger nodal melanoma deposit, higher number of melanoma involved LNs, more advanced stage and high lactate dehydrogenase (LDH) levels. Detectable ctDNA was significantly associated with worse MSS in the discovery [hazard ratio (HR) 2.11 P < 0.01] and validation cohort (HR 2.29, P = 0.04) and remained significant in a multivariable analysis (HR 1.85, P = 0.04). ctDNA further sub-stratified patients with AJCC stage III substage, with increasing significance observed in more advanced stage melanoma. Conclusion: Pre-operative ctDNA predicts MSS in high-risk stage III melanoma patients undergoing complete LN dissection, independent of stage III substage. This biomarker may have an important role in determining prognosis and stratifying patients for adjuvant treatment.