Patients undergoing lymphadenectomy for stage III melanomas of known or unknown primary site do not differ in outcome

The outcome of patients with palpable melanoma metastases in lymph nodes in the presence (metastatic melanoma of known primary site, MKP) or absence (metastatic melanoma of unknown primary site, MUP) of an identifiable primary tumour remains controversial. Some of the previous studies contained large case series that included historical patients. We aimed to compare outcomes of those with MUPs versus MKPs with palpable lymph node invasion, after staging with modern imaging technology. Aprospective study of patients from a single tertiary institution who were undergoing lymph node dissection for palpable metastatic melanoma between 2000 and 2011 was conducted. All patients were ascertained by computerised tomography scanning and most diagnosed after 2004 had positron emission tomography scanning also. Clinicopathological details about the primary melanoma and lymph node dissections were gathered. Factors associated with recurrence and melanoma-specific mortality in those with MKP and with MUP were assessed using univariate and multivariate analyses. Out of 485 patients studied, 82 had MUP and 403 had MKP. Patients were followed up for a median of 17.4 and 19.0 months, for MKP and MUP, respectively. Five-year adjusted melanoma-specific survival was 58% for MUPs versus 49% for MKPs and was not significantly different between the two groups (adjusted Cox proportional Hazard ratio = 0.88 95% confidence interval [0.58, 1.33] p = 0.54). Previously established prognostic factors such as number of positive nodes and extracapsular extension were confirmed in both sets of patients. We conclude that among melanoma patients presenting with clinically detectable nodes, when accurately staged, those without an identifiable primary lesion have similar outcomes to patients with MKP.