Electron microscopy of a nevus cell aggregate associated with an axillary lymph node.

The cellular composition of the so-called nevus cell aggregate (NCA) or inclusion has been the subject of controversy. Although the predominant opinion is that these cells are neval, some investigators suggest that they are related to glomus cells. In order to investigate this further, an NCA in the capsule of a nontumorous axillary lymph node obtained from a patient with breast cancer was removed from a paraffin block and processed for electron microscopic study. Ultrastructurally, uniform, round nevus cells with indented nuclei, dispersed chromatin, randomly oriented cytoplasmic fibrils, and a few mature melanosomes were identified. These cells closely resembled cutaneous intradermal neval cells and appeared unrelated to glomus cells. It is postulated that these NCA could be a noncutaneous anatomic source of some malignant melanomas.