Ten percent tall cells confer the aggressive features of the tall cell variant of papillary thyroid carcinoma.

BACKGROUND: The tall cell (TC) variant of papillary thyroid carcinoma (PTC) is more aggressive than classic PTC, but the percentage of TC necessary to diagnose this variant has been debated. We aimed to better determine what percentage of TC correlates with a more aggressive phenotype.

METHODS: Cases from 2005 to 2010 that were the TC variant of PTC or PTC with TC features were identified and compared with classic PTCs. All cases were reviewed to determine what percent, if any, of the tumors consisted of TC.

RESULTS: One hundred forty-one cases of PTC were reviewed. Eighty-three cases had some TC component, and 58 cases had none. There were no differences in patient demographics. Tumors with ≥10% TC had more extrathyroidal extension, angiolymphatic invasion, positive surgical margin, and lymph node involvement than classic PTC. There were more recurrences in patients with ≥10% TC, but this was not significant. Similar findings were also observed with increasing percentages of TC.

CONCLUSION: The aggressive features conferred by the presence of TC in PTCs occur with as little as 10% TC and are maintained with increasing percentages. Therefore, TC in a PTC should be reported if they comprise at least 10% of the tumor.