Focal features of papillary carcinoma of the thyroid in fine-needle aspiration material are strongly associated with papillary carcinoma at resection

The cytologic features of papillary carcinoma of the thyroid in fine-needle aspiration material have been well described. The significance of finding these features in only a small population of cells is not well characterized. I reviewed the results of 28 thyroid fine-needle aspirates processed as direct smears and cell blocks in which only a small population (<20 cells) showed features of papillary carcinoma. Papillary carcinoma was considered in 142 (8.98%) of 1,581 aspirates, and in 28 cases (1.77%), 20 cells or fewer showed features of papillary carcinoma and follow-up was available. Papillary carcinomas greater than 1 cm were identified in 11 cases (39%; 3 follicular variants), papillary carcinomas less than 1 cm were identified in 4 cases (14%), and benign lesions in the remaining 13 cases (46%). The background material (either scant or abundant benign epithelium) did not correlate significantly with the result of resection. Identifying features of papillary carcinoma in a small population of cells in either a scant or an abundant thyroid aspirate are associated with a high rate of papillary carcinomas at resection, only a minority of which represent either the follicular variant or incidental tumors.