Squamous cells in needle aspirates of subcutaneous lesions: a diagnostic problem.

Analysis of 1,000 cases of fine-needle aspiration biopsies of subcutaneous lesions revealed 430 cases diagnosed as malignant. Squamous cell carcinoma represented 37% of the malignant neoplasms, and many of these cases were highly differentiated tumors. Although the presence of keratinized squamous cells in superficial aspirates is strongly suggestive of squamous cell carcinoma, other lesions may produce atypical squamous cells on aspiration biopsy and should be considered in the differential diagnosis. These include acanthotic ameloblastomas, metaplastic adenocarcinomas and Warthin's tumors, branchial cleft cysts, odontogenic keratocysts, and epidermal inclusion cysts. Two-needle aspirates from these cases were incorrectly interpreted as squamous cell carcinoma. The cytologic and some of the histologic characteristics of these lesions that may pose a diagnostic problem are presented. Careful evaluation of nuclear and cytoplasmic features, cellular background, clinical findings, and history is essential to avoid a false positive diagnosis of squamous cell carcinoma.