Large plaque-type blue nevus with subcutaneous cellular nodules

Unusual or atypical melanocytic nevi can be confused with malignant melanom a. The authors present two cases of an unusual variant of blue news that we re misdiagnosed initially as malignancy. Both lesions were asymptomatic and characterized clinically by childhood onset, with slow enlargement during adolescence and subsequent nodule formation. One lesion, which measured 24 cm in greatest dimension, was located on the anterior chest wall of a 53-ye ar-old woman. The other lesion, which measured approximately 15 cm in great est dimension, was located on the lateral abdominal wall of a 20-year-old m an. Both lesions were characterized by a multifocal dermal and subcutaneous proliferation of fusiform and dendritic pigmented melanocytes. The histolo gic appearance of individual foci ranged from dermal melanocytosis to commo n blue nevus and cellular blue nevus. The cellular foci were located in the subcutis and involved, in one patient, the stroma of the breast. The cells were immunoreactive For S-100 protein, gp100 (HMB-45), and Melan-A (A103). Ultrastructural analysis revealed melanocytes typical of blue nevus. The w oman underwent complete excision of the lesion, and the man underwent only partial excision of the lesion. On clinical follow-up of 32 and 19 months, respectively,both patients are alive and well with no evidence of recurrenc e or progression. Because the lesions presented clinically as large plaques and were diagnosed histologically as blue nevi with subcutaneous foci of c ellular blue nevus, we term this rare variant of blue news large plaque-typ e blue nevus with subcutaneous cellular nodules. Recognition of this lesion enhances our knowledge of the morphologic spectrum of melanocytic tumors a nd helps to avoid confusion with malignant melanoma.