Atypical or worrisome features in cellular neurothekeoma: a study of 10 cases.

Cellular neurothekeoma is a recently characterized benign cutaneous neoplasm arising usually on the upper trunk or head and neck of children or young adults. Typical histology is that of a lobulated dermal tumor composed of spindle and epithelioid cells, arranged in fascicles and nests, lacking immunoreactivity for S-100 protein, but usually being NK1/C3 positive. We present 10 new cases of cellular neurothekeoma with atypical histologic features that have not been described previously and that suggested the possibility of malignancy. The age range of affected patients was 1 to 44 years (median, 20.5 years); sites included the head and neck (three cases), the upper limbs (two cases), the lower limbs (two cases), and the trunk (two cases). Atypical findings in individual cases included large size (up to 6 cm), deep penetration (extending into skeletal muscle or subcutaneous fat, or both), diffusely infiltrative borders, vascular invasion, high mitotic rate, and marked cytologic pleomorphism. Clinical follow-up was available in 7 of 10 cases. Although the atypical features raised concern about the biologic potential of these lesions, preliminary follow-up (1-5 years) has shown no recurrence and suggests that complete surgical excision of these lesions is curative. These new data expand the morphologic spectrum of cellular neurothekeoma.