1245 Statistical modeling of naevus distribution for melanoma risk stratification

Two recent studies have shown that the distribution of naevi >5mm on the back tend to cluster in melanoma high risk cohorts, while complete spatial randomness is seen in the general population. Hence, the spatial distribution of naevi on the body could be used to identify high risk individuals. To understand the distribution patterns of >2mm naevi in general population adults, we used 3D total body images from a prospective longitudinal study of naevi in 149 adults in Queensland, Australia. The spatial scan statistic and the Ripley’s K function were used to visualize the distribution patterns of naevi on the anterior and posterior surface of the body separately, and to identify hotspots and clusters. Preliminary results from the posterior surface indicated that while no statistically significant hotspots were identified, 91% (136) appeared to have at least one naevus cluster. Clusters of naevi were more commonly seen on the upper third of the back for both men (23%, 21/93) and women (34%, 19/56). This was followed by the upper arms in women (23%, 13/56), and the middle third of the back in men (22%, 20/93). When the K function was adjusted for the inhomogeneity of the prevalence of naevi across body sites in each individual, the distribution of naevi >2mm on the posterior surface seemed to show complete spatial randomness in a randomly selected local area of approximately 25cm in diameter. However, when considering larger areas up to covering the complete posterior surface of the body the distribution seemed to be uniform. These distribution patterns did not differ by sex or age. By comparing these results with further studies in high-risk cohorts, naevus distribution patterns could be used as an additional independent predictor of melanoma risk leading to earlier detection of melanoma and improved patient outcomes.