Nodular melanoma is less likely than superficial spreading melanoma to be histologically associated with a naevus.

OBJECTIVES

To determine the frequency of naevus-associated melanoma among superficial spreading and nodular subtypes; and to investigate associations between naevus-associated melanoma and other clinico-pathological characteristics.

DESIGN, SETTING AND PARTICIPANTS: Cross-sectional study of all patients with nodular and superficial spreading melanomas diagnosed between 1994 and 2015 at the Victorian Melanoma Service, Melbourne.

METHODS AND MAIN OUTCOME MEASURES

Clinical and pathological characteristics of naevus-associated and de novo melanomas were assessed in univariable and multivariable logistic regression analyses.

RESULTS

Of 3678 primary melanomas, 1360 (37.0%) were histologically associated with a naevus and 2318 (63.0%) were de novo melanomas; 71 of 621 nodular (11.4%) and 1289 of 3057 superficial spreading melanomas (42.2%) were histologically associated with a naevus. In multivariable analyses, the odds of being associated with a naevus were higher for melanomas located on the trunk (v head and neck: adjusted odds ratio [OR], 2.27; 95% CI, 1.73-2.96; P < 0.001), while the odds were lower for thicker tumours (adjusted OR, 0.75 per millimetre increase in Breslow thickness; 95% CI, 0.69-0.81; P < 0.001), amelanotic/hypomelanotic melanomas (adjusted OR, 0.68; 95% CI, 0.48-0.97; P = 0.035), and older age (patients 70 years or older v patients under 30 at diagnosis: adjusted OR, 0.28; 95% CI, 0.20-0.40; P < 0.001). After adjusting for confounders, the odds of an associated naevus was three times as high for superficial spreading melanomas as for nodular melanomas (adjusted OR, 3.05; 95% CI, 2.24-4.17; P < 0.001).

CONCLUSION

Melanomas are most likely to arise in the absence of a pre-existing naevus, particularly nodular melanomas. Public health campaigns should therefore emphasise the detection of suspicious de novo lesions, as well as of changing lesions.