Oncocytic (Hurthle cell) tumors of the thyroid: Distinct growth patterns compared with clinicopathological features

Neoplastic growth results from cell production that exceeds cell loss. We r egistered mitotic and apoptotic indices (MT and AI) in 97 immunohistochemic ally verified oncocytic (Hurthle cell) tumors of the thyroid (OT; 50 adenom as [OA], 20 atypical adenomas [aOA], and 27 carcinomas [OC]) and compared t hese kinetic data with histological diagnoses and other parameters. MI, alt hough very low in all, was significantly higher in carcinomas than in adeno mas. Conversely, AI did not differ as much among the 3 groups. This indicat es that the magnitude of cell deletion did not play a prominent role in det ermining the disparate growth of the 3 types of oncocytic tumors. Cluster a nalysis with MI and AI per case as variables revealed the existence of 3 gr oups of neoplasms with highly distinct growth characteristics: (1) near-ste ady state (n = 78, all diagnostic categories represented); (2) progressive (n = 9, mostly carcinomas); and (3) regressive (n = 10, mostly adenomas). M I distinguished between histologically benign and malignant with the greate st discriminant power of the variables tested. Proliferative indices should thus be included in the differential diagnostic evaluation of oncocytic th yroid tumors. Our study also suggests that invasiveness and growth are 2 di verging properties of carcinomas.