Aspiration biopsy cytology of primary cutaneous tumors.

Primary cutaneous neoplasms may undergo fine needle aspiration during the workup of patients with suspected metastatic disease. Such aspirates present a wide range of epithelial and nonepithelial proliferations that must be separated from more common metastatic deposits. The majority of primary cutaneous tumors are composed of squamous or basaloid cells that can be confused with metastatic squamous cell carcinoma. In addition, primary cutaneous lymphomas and mesenchymal tumors morphologically overlap their more common systemic or metastatic counterparts in appearance. Both clinical and cytologic features aid in the differentiation of pilomatrixomas, basal cell carcinomas, sebaceous carcinomas, primary squamous cell carcinomas, Merkel cell tumors and epidermal inclusion cysts from metastatic squamous cell carcinomas. The presence of small basaloid cells in an aspiration smear favors the diagnosis of a primary neoplasm, such as pilomatrixoma or basal cell carcinoma. Clinical findings and cell marker studies are important in the cytologic diagnosis of primary cutaneous lymphomas. Complex convolutions in the nuclei of neoplastic lymphoid cells favor a primary cutaneous origin. We report the cytologic features of 94 primary cutaneous tumors seen in a series of 558 aspirates of subcutaneous and cutaneous nodules.