Malignant blue nevus with lymph node metastases

Background:  Malignant blue nevi arise within cellular blue nevi and contain atypical mitoses, necrosis, nuclear pleomorphism and prominent nucleoli. Malignant blue nevus has been described as a distinct identity, a rare form of malignant melanoma, and a misdiagnosed melanoma.Methods:  We present a patient with metastatic malignant blue nevus and studies on the histopathologic, immunohistochemical, and molecular features of the neoplasm.Results:  Histology showed a malignant blue nevus arising in a combined intradermal and cellular blue nevus. CD117 (c‐kit) staining showed diffuse cytoplasmic expression within the cellular blue nevus, decreased staining in the malignant component, and variable positivity within the lymph node metastases. Molecular loss of heterozygosity analysis showed different allelic patterns at the hOGG‐1 locus between the melanoma and control skin specimens with a varying heterozygous allelic pattern in both the benign and malignant blue nevus.Conclusions:  Our case of malignant blue nevus with lymph node metastasis involved mutation of the hOGG‐1 DNA repair gene. CD117 showed decreased staining of the primary malignant blue nevus with marked upregulation in the metastatic lesion, unlike most metastatic melanomas. Further study is needed to determine if hOGG‐1 mutation or c‐kit upregulation play a role in the pathogenesis of dendritic melanocytic lesions (either benign or malignant).