Abstract:

Classifying melanocytic neoplasms can present a diagnostic challenge; validation of alternate ancillary tests would be useful. Primary cilia are cell surface organelles that have been shown to reliably differentiate melanoma, which fail to ciliate, from melanocytic nevi, which retain primary cilia. This study expands on prior work validating the ciliation index as an ancillary test in a broader range of histopathologically challenging melanocytic neoplasms. We collected 80 cases for which aCGH was performed. Our cohort included spitzoid, blue nevus-like, BAP1-loss, ALK-fusion, NTRK-fusion, deep penetrating nevus-like, and conventional melanocytic neoplasms. These cases were divided into ‘benign’ (n=12), ‘atypical’ (n=48) and ‘malignant’ (n=20) groups based on final diagnosis. A triple antibody cocktail (SOX-10, gamma-Tubulin, acetylated alpha-Tubulin) with immunofluorescent secondary antibodies was used to label the melanocytes, centrioles and ciliary axoneme for each case. The average ciliation index for the benign group was significantly higher than the malignant group (p<0.0001); 78% versus 15%, respectively. Lesions in the atypical group showed a bimodal distribution of ciliation: 19 cases showed less than 20% and 22 cases had between 73-100% ciliation. Upon independent histopathologic re-examination of the bimodal atypical group by two expert dermatopathologists (THM & PEL), only 5 of the cases were favored to be severely atypical with an average ciliation index of 6% and 13 cases were found to have minimal atypia with an average ciliation index of 88%. A significant number of atypical cases (n=24) remained ‘undecided’ based purely on histopathology alone. There are ongoing efforts to collect clinical outcomes data to further examine the biologic significance of the bimodal distribution of the ciliation index. Our results lend further support to using ciliation index as an adjunct morphologic tool in a wide spectrum of histopathologically challenging cases.

Financial Disclosure: No current or relevant financial relationships exist.

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Kathleen Sheahon, MD