Papillary Thyroid Carcinoma with Hobnail Features: Histopathological Criteria To Predict Aggressive Behavior

Background: Recent reports indicate that papillary thyroid carcinoma (PTC) with hobnail features (micropapillary variant of papillary thyroid carcinoma, MPTC) is a rare, but very aggressive variant of PTC. We examined 23 cases of MPTC to determine the prognostic signifi cance of the amount of micropapillary or hobnail features in these tumors. Design: The histopathological and immunohistochemical features of 23 MPTC were examined. Follow up information was obtained from medical record review. The patients included 17 females and 6 males. Ages ranged from 28 to 78 (mean 57). Tumor size ranged from 1 to 5.8 cm (mean 3 cm). The average follow-up time was 106 months (range: 4 to 272 months). Results: Twelve cases (52.2%) of MPTC showed more than 30% micropapillary or hobnail features and all but 3 cases were associated with an aggressive behavior during follow-up. In particular, all but two cases showed lymph node metastases at presentation. During follow-up, 6 of these patients died of disease after a mean of 44.8 months and 3 patients remained alive with extensive disease involving the epiglottis, larynx, and nasopharynx in two cases and the shoulder, lung, bone, muscle, and pancreas in one case after a mean follow-up of 32.3 months. The other 3 patients with prominent micropapillary or hobnail features were alive without evidence of disease after a mean follow-up of 125.3 months.The other 11 PTC cases (47.8%) showed less than 30% micropapillary or hobnail features. Eight of these patients were alive without disease after a mean of 169 months and one patient died of sepsis which was not related to thyroid tumor after 155 months. Two patients in this group died of disease after 21 and 163 months respectively. Conclusions: These fi ndings confi rm earlier observations that MPTC is an aggressive variant of PTC. Tumors with more than 30% hobnail features were often very aggressive, although two patients with tumors with less than 10% hobnail features also had poor outcomes