Polyploidy in spitz nevi: a not uncommon karyotypic abnormality identifiable by fluorescence in situ hybridization.

Fluorescence in situ hybridization (FISH) often reveals imbalanced chromosomal gains in melanoma, whereas Spitz nevi typically have a normal complement of chromosomes. However, there may be a subset of Spitz nevi that are perfectly tetraploid by FISH analysis, and these cases may be confused diagnostically with melanoma. This study evaluates 41 cases of Spitz nevi that were histologically confirmed to be benign. Four of these lesions demonstrated polyploidy by FISH. Three of the 4 cases were from the same patient, a 17-year-old woman; 1 lesion was from the wrist, whereas the other 2 were from the buttocks. The other case was from a 14-year-old man from the ankle. All 4 cases that were polyploid were confirmed using a probe for the X chromosome. This article highlights the importance of polyploidy as a feature of some benign Spitz nevi.