Hurthle cell tumors are thought to be variants of follicular neoplasms. However, they are more difficult to treat than the usual follicular neoplasms for several reasons (35): 1) the incidence of carcinoma varies from 5.3% to 62% in different clinical series; 2) benign-appearing tumors later metastasize in up to 2.5% of patients; and 3) Hurthle cell cancers are far less likely to concentrate radioiodine than are the usual follicular carcinomas, which makes treatment of metastatic disease particularly difficult.

Of 54 patients with Hurthle cell tumors whom we treated (38), 4 had grossly malignant lesions, 10 had questionable diagnoses (“intermediate” lesions) because of partial penetration of their capsule by tumor, and 40 (74%) had lesions that were thought to be benign. About half the patients had a history of low-dose external irradiation; many had separate papillary or follicular cancers in the same thyroid gland.

During a mean follow-up period of 8.4 years, three additional Hurthle cell tumors were recognized as malignant after metastases were discovered: Two were originally classified as intermediate lesions, and one was in the benign-appearing group. Thus, 7 of 54 (13%) of our patients who had a Hurthle cell tumor had Hurthle cell carcinoma. One of the 7 patients with Hurthle cell cancer died of widespread metastases after 35 years, and the other 6 are currently free of disease.

We believe that treatment of these lesions should be individualized (38,39). Total thyroid ablation is appropriate for frankly malignant Hurthle cell cancers, for all Hurthle cell tumors in patients who received low-dose childhood irradiation, for patients with associated papillary or follicular carcinomas, for all large tumors, and for patients whose tumors exhibit partial capsular invasion. On the other hand, single, well-encapsulated, benign-appearing Hurthle cell tumors that are small may be treated by lobectomy and careful follow-up because the chance that they will later exhibit malignant behavior is low (2.5% in our series and 1.5% among patients described in the literature) (38). Nuclear DNA analysis may aid the surgeon in recognizing tumors that are potentially aggressive because such tumors usually demonstrate aneuploidy (40). Furthermore, increased genetic abnormalities have been shown in Hurthle cell carcinomas when compared with Hurthle cell adenomas (41).

In a review of follicular cancers at The University of Chicago (39), the overall mortality was 16%, twice that of papillary carcinomas. However, in non-Hurthle cell follicular cancers the mortality was 12%, whereas in Hurthle cell cancers it was 24%, thus demonstrating the difficulty in treating metastatic disease which cannot be resected in the Hurthle cancer.