Abstract

An adenomyoepithelioma (AME) is a biphasic tumor consisting of a neoplastic epithelial and myoepithelial population. These benign lesions typically present as solitary nodules in the female breast. We present a case of an AME arising within a congenital melanocytic nevus in a 15 year-old male, mimicking malignant transformation clinically and histopathologically. The patient had a longstanding congenital melanocytic nevus on the scalp and presented to dermatology with the development of a new, rapidly growing nodule within it. Microscopic sections showed a background congenital nevus with a distinct, deeply located nodule comprised of atypical epithelioid cells with cytoplasmic vacuoles and an increased mitotic index seated within myxoid stroma. The background nevus as well as the nodule expressed SOX-10. Additional immunostains showed that the epithelioid cells expressed EMA but lacked MART-1 and pancytokeratin expression. The nodule showed an increased Ki-67 cell proliferation index as compared to the adjacent nevus. Given the immunophenotype in conjunction with the morphology, the resulting diagnosis was adenomyoepithelioma arising within a congenital nevus. This is an extremely rare entity and an important mimic of malignancy, especially when arising in the background of a melanocytic lesion. Additionally, whether there is a causal relationship between these two entities is deserving of further investigation.

Financial Disclosure:
No current or relevant financial relationships exist.