Microvessel count: an indicator of poor outcome in medullary thyroid carcinoma but not in other types of thyroid carcinoma.

The growth of newly formed vessels (neoangiogenesis) represents an important step both in physiologic and pathologic situations. In particular, tumor growth and metastasis require angiogenesis. Microvessel count, which expresses a measure of tumor angiogenesis, has been associated with metastatic spread in cutaneous, mammary, prostatic, head, neck, and pulmonary cancer. In this study, the role of tumor angiogenesis as a prognostic indicator was examined in 157 primary thyroid cancers including 82 well-differentiated carcinomas, 52 medullary carcinomas, and 23 undifferentiated carcinomas. Microvessels were carefully counted by highlighting endothelial cells with anti-CD34 formalin-fixed tumor samples. The mean of microvessel count was 30.7 per field in papillary thyroid carcinomas, 39.4 per field in follicular thyroid carcinomas, 32.7 per field in undifferentiated carcinoma, and 41.8 per field in medullary carcinoma. We found that the number of newly formed vessels was significantly associated with poor prognosis only in medullary carcinoma. All of the dead patients with medullary carcinoma showed a microvessel count higher than 30, which resulted in a high statistical difference compared with alive patients (P = 0.00098). Multiple logistic regression analysis showed microvessel count, together with pTNM (P = 0.026). These results were also confirmed by Kaplan-Meir survival analysis (log-rank test; P = 0.04). By contrast, no differences in the number of microvessels was found between dead and living patients with well-differentiated carcinoma and undifferentiated carcinoma. In conclusion, microvessel count, as quantitation of tumor angiogenesis, plays an important prognostic role in medullary thyroid carcinomas.