Melanoma with benign melanocytic naevus components: reappraisal of clinicopathological features and prognosis.

The clinicopathological features and prognosis of primary cutaneous malignant melanoma with benign melanocytic naevus (BMN) components are still under debate. The purpose of this study was to characterize further the clinical and histopathological features of naevus-associated melanomas, with emphasis on the BMN components, and to examine their prognosis based on a large series. Following a histopathological review of 667 consecutive cases of primary cutaneous melanoma, 148 melanomas with BMN components (22.1%) were identified for further study. A control group of 519 melanomas without BMN components seen in a similar period were also studied. Clinically, patients with melanomas containing BMN components (n = 148; age range 25-86 years, mean age 54 +/- 16 years; male to female ratio 1:1.02) presented with tumours located mainly on the trunk (34.5%), followed by the upper extremities (24.3%), lower extremities (20.3%), and head and neck (14.2%). Compared with tumours without BMN components (n = 519; age range 19-89 years, mean age 57 +/- 15 years; male to female ratio 1:1.3), melanomas with BMN components occurred in slightly younger individuals (P = 0.027). Histopathologically, BMN components mainly showed features of acquired naevi (total 87 cases; dysplastic, 80 cases; banal, seven cases) or congenital naevi (total 57 cases; superficial, 56 cases; deep, one case), but a minority of these lesions (four cases) could not be further subcategorized. Generally, melanomas containing BMN components were relatively thinner than melanomas without BMN components (mean Breslow index 0.95 +/- 0.83 mm and 1.3 +/- 1.6 mm, respectively) (P = 0.015). The follow-up data available in 69 patients with naevus-associated melanomas consistently revealed a relatively good outcome (5 year metastasis-free survival rate 93.75%), although no statistical difference in prognosis was observed between this group and a subset of 283 melanomas patients without BMN components stratified by tumour thickness. We conclude that BMN components in naevus-associated melanomas constitute a heterogeneous group morphologically, consisting mainly of dysplastic and superficial congenital naevi. This finding indicates a more important role for superficial congenital naevus as a precursor lesion of naevus-associated melanomas than presently recognized. Patients with naevus-associated melanomas generally show a good clinical outcome, reflecting their small Breslow index.