Neurotropic melanoma: an analysis of the clinicopathological features, management strategies and survival outcomes for 671 patients treated at a tertiary referral center.

Neurotropic cutaneous melanoma is a rare melanoma subtype that invades nerves and is often associated with desmoplastic melanoma. Limited data suggest that it has a greater propensity to recur locally, but it is unknown whether its behavior differs from that of other melanoma subtypes, including desmoplastic melanoma. We investigated clinicopathological predictors of outcome in a cohort of 671 patients with neurotropic melanoma to develop evidence-based management recommendations. Patients with primary neurotropic melanoma diagnosed from 1985 to 2013 were identified from the Melanoma Institute Australia database, along with a control cohort of 718 non-neurotropic melanoma patients. Features predictive of sentinel lymph node status, recurrence, melanoma-specific survival and response to adjuvant radiotherapy were sought. Neither local recurrence (hazard ratio: 1.28 (0.73-2.25) P=0.39) nor melanoma-specific survival (hazard ratio: 0.79 (0.55-1.15) P=0.22) were significantly affected by the presence of neurotropism on multivariate analysis. However, there was a markedly reduced likelihood of sentinel node positivity (hazard ratio: 0.61 (0.41-0.89) P=0.01) in neurotropic melanoma patients. Surgical margins ≥8mm halved the recurrence risk compared with <2 mm margins (hazard ratio: 0.46 (0.31-0.68) P<0.001). Additionally, in neurotropic melanoma patients with <8 mm margins, adjuvant radiotherapy halved the recurrence risk (hazard ratio: 0.48 (0.27-0.87) P=0.02). This, the largest study of neurotropic melanoma reported to date, has demonstrated that the presence of neurotropism does not alter the risk of melanoma recurrence or survival but does reduce the likelihood of sentinel node positivity. For successful treatment of neurotropic melanoma, adequate excision margins are of paramount importance. However, when adequate margins cannot be achieved, adjuvant radiotherapy reduces the risk of recurrence.