Pathologic study and clinical significance of Hürthle cell papillary thyroid carcinoma

Hürthle cell papillary thyroid carcinoma is a variant of papillary thyroid carcinoma (PTC). Its pathologic and clinical significance has not been well documented. The authors studied the relative incidence of Hürthle cell PTC and the relationship of Hürthle cell PTC to other variants of thyroid carcinoma. Three hundred eighty consecutive cases of thyroid carcinoma were reviewed to identify cases with focal or extensive areas of Hürthle cell PTC, classic PTC, Hürthle cell carcinoma (ie, non-Hürthle cell PTC), and follicular carcinoma. In addition, the status of lymphoid infiltrate in the tumor, stromal invasion with desmoplastic reaction, vascular invasion, and distant and lymph node metastasis were noted by microscopic examination, review of clinical charts, or both. A total of 24 (HCs) and 42 PTCs with Hürthle cells were identified. The latter category was divided into pure Hürthle cell PTC or extensive Hürthle cell (HPTC) (28 cases) and PTC or Hürthle cell carcinoma with focal areas of Hürthle cell PTC (14 cases). The Hürthle cell PTC/Hürthle cell carcinoma ratio was lower than that of PTC/follicular carcinoma (39:289) (P = 0.001). Follicular or solid structures were present in all HPTCs. HPTCs were associated with frequent stromal intrathyroid and extrathyroid invasion, but they tended to have a lower rate of lymph node metastasis (8/28) compared with classic PTC with stromal invasion (108:200) (P = 0.12) and a lower rate of distant metastasis (2:28) compared with Hürthle cell carcinoma (15:24) (P = 0.02) or follicular carcinoma (13:39) (P = 0.04). Warthin-like Hürthle cell PTC (10 cases) was associated with extrathyroid invasion in five cases. In Hürthle cell PTC associated with tall cell variant (10 cases), areas of gradual transition between Hürthle cell PTC and tall cell variant were identified. The latter variant showed the highest rate of extrathyroid stromal and vascular invasion with distant metastasis and patient death compared with all Hürthle cell PTCs and classic PTCs. In conclusion, Hürthle cell PTC is frequently associated with tall cell variant. It has a higher potential for extrathyroid invasion than classic PTC and has vascular invasion and distant metastasis characteristics intermediate between those of classic PTC and Hürthle cell carcinoma with or follicular carcinoma. Hürthle cell PTC tends to show a greater likelihood of extrathyroid invasion when associated with Warthin-like features and tall cell variant PTC, and higher vascular invasion and distant metastasis when associated with tall cell variant.