Although Hürthle cell tumors are considered to be variants of follicular neoplasms, they have distinct cytologic and behavioral characteristics. To elucidate the basis for these differences, the expression of 5 oncogenes and growth factors (Pan-ras, N-myc, transforming growth factor-α [TGF-α], transforming growth factor-β [TGF-β], and insulin-like growth factor 1 [IGF-1]) was compared between 12 follicular carcinomas and 8 Hürthle cell carcinomas by immunocytochemistry. The percentage of follicular carcinomas and Hürthle cell carcinomas that stained positively for the different oncogenes was as follows and respectively: Pan-ras 8% versus 63%; TGF-α 17% versus 63%; TGF-β 25% versus 88%; IGF-1 17% versus 88%; and N-myc 17% versus 100%. All these differences were highly significant by the X2 test. This difference in the expression of oncogenes between Hürthle cell carcinomas and follicular carcinomas suggests that these two tumors could, in fact, represent separate entities.
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