Purpose: Controversy exists over the ability of morphology to predict the biologic behavior of Hürthle cell carcinoma. The aim of this study was to conduct a critical histopathologic review of Hürthle cell carcinoma and to correlate morphologic parameters with clinical outcome.
Patients and methods: Patients with histologically confirmed Hürthle cell carcinoma treated between 1940 and 2000 form the basis of this study. Adenomas were excluded. Tumors of unknown malignant behavior ([UMB] n = 17) had solid growth pattern, incomplete capsular invasion (Ci), or both but no vascular invasion (Vi). Minimally invasive carcinomas ([MIC] n = 23) had one focus of intra- or extracapsular Vi, one focus of complete Ci, or both. Widely invasive carcinomas ([WIC] n = 33) demonstrated more than one focus of Vi, more than one focus of Ci, or both. The primary end points were relapse-free survival (RFS) and disease-specific survival (DSS). Rates of recurrence/death were estimated by Kaplan-Meier method. The univariate influence of prognostic factors on end points was analyzed by log-rank test, and multivariate analysis was performed by Cox regression.
Results: Median follow-up was 8 years. No patients with UMB or MIC relapsed or died of disease. Of WIC, 73% relapsed and 55% died of disease. Age, size, and extent of resection did not influence outcome. Adverse predictors of RFS and DSS among WIC were extrathyroidal extension, nodal metastasis, positive margin, and solid growth pattern (P <.05). Both Ci and Vi were associated with worse DSS (P <.05). On multivariate analysis, extrathyroidal extension and nodal metastases were independent predictors of outcome (P <.05).
Conclusion: Patients with Hürthle cell carcinoma have a prognosis that is predicted by well-defined histomorphologic characteristics. Unlike differentiated thyroid cancer, nodal metastases predict a worse outcome in widely invasive Hürthle cell carcinoma, as does extrathyroidal extension.