Extraordinary Case ReportAtypical Cellular Blue Nevus With Necrosis Mimicking Melanoma Ex-Blue NevusHenning, Ania MD*; Billings, Steven MD†; Ko, Jennifer MD†; Weaver, Joshua MD*Author Information *Department of Pathology and Laboratory Medicine, Summa Health System, Akron City, OH; and †Department of Anatomic Pathology, Cleveland Clinic, Cleveland, OH. Correspondence: Ania Henning, MD, 525E Market Street, Akron, OH 44304 (e-mail: [email protected]). The authors declare no conflicts of interest. The American Journal of Dermatopathology: May 2021 - Volume 43 - Issue 5 - p e61-e64 doi: 10.1097/DAD.0000000000001913 Buy Metrics Abstract Histologic distinction between melanoma ex-blue nevus and cellular blue nevus (CBN) can often be difficult, but features supporting melanoma include infiltrative growth pattern, frequent mitoses, cytologic atypia and pleomorphism, cell crowding, and tumor necrosis. Unfortunately, these features are not constantly dependable and frequently borderline lesions exist, so-called atypical CBN, which lack explicit malignant features. Furthermore, some CBN and atypical CBN show an assortment of features, which may lead to their misdiagnosis as melanoma, but to date necrosis is generally absent. We present an unusual case of an atypical cellular blue nevus with extensive necrosis mimicking melanoma ex-blue nevus. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.