Oncocytic cell tumors of the thyroid: factors predicting malignancy and influencing prognosis, treatment decisions, and outcomes.

Background: The distinction between malignant and benign thyroid oncocytic cell tumors (OCTs) before and during surgery still represents a diagnostic challenge. We focused on the search for specific factors that predict malignancy and influence the prognosis of OCTs, and for their most appropriate management.

Methods: From January 1998 to May 2007, 57 patients underwent thyroidectomy in our surgical department because of OCT. A cross-sectional study of 28 patients with carcinoma and 29 patients with adenoma was performed: demographic data, tumor characteristics, diagnostic results, patient management, postoperative, and follow-up results were evaluated.

Results: The prevalence of malignancy was 49.1%. The mean tumor size was significantly greater for carcinomas than for adenomas (3.0 cm vs. 1.8 cm; p = 0.003). Threshold sizes of more than 3.0 cm and 4.0 cm were significant for predicting malignancy (p = 0.020 and p = 0.010, respectively). Tumor multifocality, microfollicular features, and severe cytological atypia also were significantly related to malignancy (p = 0.012 and p = 0.025, respectively). Recurrent OCT was observed in three patients with carcinoma. One patient with distant metastases died from the disease. Older age, tumor size, thyroid capsular invasion, higher TNM stage, and AMES high risk were factors significantly related to tumor recurrence. Multivariate analysis showed that larger tumor size was the only factor predictive of malignancy and influencing recurrence.

Conclusions: All OCTs should be referred to surgery because of the high prevalence of malignancy. In the case of OCTs with larger tumor size and microfollicular features with severe cytological atypia, total thyroidectomy is strongly recommended as initial treatment also in relation with the more likely aggressive biological behavior of greater tumors.