RESUMEN
INTRODUCTION: The histological and immunohistochemical profile of medullary thyroid carcinoma is ill-defined. The objective of this study was to determine the epidemiological, histological, and immunohistochemical characteristics of medullary carcinoma and to analyze whether differences exist between sporadic and familial carcinomas. PATIENTS AND METHODS: Fifty-five histologically confirmed tumors were studied. Histological slides were reviewed and immunohistochemical staining of the archival paraffin blocks was performed. RESULTS: Nineteen of the 55 carcinomas (35%) were sporadic, and 36 (65%) familial. Sex distribution was similar, but familial carcinoma was more common in patients under 40 years of age (p<0.001). A solid growth pattern and plasmacytoid cells were found in most cases. C-cell hyperplasia and multicentricity were more frequent findings in familial carcinoma, while tumor necrosis, hemorrhagic foci, vascular invasion, and neovascularization were more common in the sporadic type. Immunohistochemical staining was positive for calcitonin, CEA, bcl-2, and p53 protein. With regard to staging, familial carcinomas were diagnosed in the earliest stages, when they were smaller and there were no lymph node metastases (p<0.01). CONCLUSIONS: Familial cases were more frequent when there was more C-cell hyperplasia and multicentricity. Sporadic cases more frequently showed foci of necrosis, hemorrhage, vascular invasion, and neovascularization. Neither histopathological nor immunohistochemical criteria are useful for differentiating between familial and sporadic forms.