Inverse association between the total nevus count and melanoma thickness

BACKGROUND: Individuals with a high total nevus count (TNC) are at a higher risk to develop melanoma and screening efforts have been largely focused on this group. However, some studies suggest that melanomas of patients with many nevi are thinner than those of patients with few nevi. Additionally, nodular melanoma has been associated with individuals with a low nevus count. OBJECTIVE: To investigate the association between TNC and melanoma Breslow thickness METHODS: A two-center retrospective study from January 1, 2016 to January 1, 2018. This included three hundred twenty-six consecutive melanoma patients from two tertiary melanoma centers. The mean age at presentation was 58.3 years (SD=15.9) and the majority (54.9%, N= 179) were women. Incidence of new in situ and invasive melanomas and correlation with TNC were measured. RESULTS: The mean total nevus count for patients presenting with in-situ melanoma was 57.2 (range 4 - 178), while for patients presenting with invasive disease was 31.5 (P=0.01). In situ disease was associated with a higher TNC across all ages. For invasive melanoma, a positive association between age and Breslow thickness was observed, while TNC was inversely associated with Breslow thickness. Each additional nevus accounted for a 4% decreased likelihood that the subject had invasive disease. CONCLUSION: Patients with a higher nevus count had thinner melanomas and more melanomas in-situ, independent of age and sex.