Abstract
Ciliation index (CI) is defined as the percentage of lesional cells with a primary cilium (PC), a ubiquitous organelle found on the apical surface of almost all cell types.1 Low CI has been demonstrated in in several melanomas, but their retention has not been studied in nevoid melanoma and PRAME-negative or –indeterminant melanoma.2-7 Fluorescent immunohistochemistry (IHC) was done in 9 nevoid melanomas and 8 mitotically active melanocytic nevi, as well as 4 PRAME-negative melanomas, 4 PRAME-indeterminant melanomas, 5 PRAME-positive melanomas, and 3 PRAME-negative benign melanocytic nevi. The CIs were compared using an independent t-test. Low CI was demonstrated in all 4 nevoid melanomas relative to mitotically active melanocytic nevi, as well as in all but one PRAME-negative melanoma and the PRAME-indeterminant melanomas relative to benign melanocytic nevi. These suggest that CI can be a helpful adjunct to distinguish nevoid melanoma from mitotically active nevi, and when the histopathology and PRAME IHC results are not congruent.