Abstract

A 72-year-old female presented with a tender and “slow-growing” scalp mass. The patient first noticed the mass five years ago and denies any associated symptoms. Her previous cancer screening studies were unremarkable. Physical examination revealed a 2-cm pink, pearly, ovoid nodule on the left posterior scalp. Shave biopsy of the mass showed the surface of a dermal neoplasm with glandular differentiation that stained positive for CK7 and negative for CK20. CT scan of the chest showed tiny non-specific nodules. A metastatic adenocarcinoma from the lung was suspected. However, complete excision of the lesion revealed a well-circumscribed dermal nodule consisting of clusters of epithelioid cells appearing as duct-like structures that are embedded in a hyalinized stroma with areas of fatty metaplasia. The cells’ nuclei are ovoid, vesicular and mildly pleomorphic and have abundant pale-eosinophilic cytoplasm. Mitoses, marked nuclear atypia and necrotic areas were not identified. Immunohistochemical studies of the neoplastic cells demonstrated a Ki-67 proliferation index of less than 1% and positivity for AE1/3, calponin and S-100.  A diagnosis of cutaneous myoepithelioma was rendered. Cutaneous myoepithelioma is a rare and underrecognized benign neoplasm of the skin and soft tissue that typically responds completely with excision. In our case it was initially thought to be a metastatic adenocarcinoma in the skin due to partial sampling and its unusual “duct-like” architecture. This resulted in extensive metastatic workup, undue anxiety and radiation exposure from imaging and increased healthcare expenditures. It is imperative for pathologists to recognize this uncommon benign entity for optimal patient care.