Bone metastases from thyroid carcinoma: a histopathologic study with clinical correlates.

CONTEXT Only limited information exists on the pathologic aspects of thyroid carcinomas with bone metastases, most large studies having concentrated mainly on their clinical features. OBJECTIVE To study in detail the morphologic features of thyroid carcinomas with skeletal metastases. DESIGN Seventy-nine cases of thyroid carcinoma with bone metastases treated at Memorial Sloan-Kettering Cancer Center, New York, NY, between 1964 and 1998 were investigated, with emphasis on the pathology of the primary and/or metastatic tumors and comparison of the morphologic features of the tumors at both the sites, wherever possible. The tumors were also compared for various clinical parameters. RESULTS The cohort consisted of 22 papillary, 17 follicular, 16 insular, 10 anaplastic, 9 Hürthle cell, and 5 medullary carcinomas. Of these cases, 68% had poorly differentiated or undifferentiated features in the primary and/or metastatic tumors. The metastatic tumors were better differentiated than the primary in one third of the cases (6 of 18). Only one case showed a less differentiated metastasis. The overall 5- and 10-year survival probabilities after the bone metastases were 29% and 13%, respectively (Kaplan-Meier method). Although both the tumor type and differentiation seemed to affect survivals after bone metastasis (P =.007 and.012, respectively) (log-rank test), this was primarily due to the much worse prognosis in the cases of anaplastic and medullary carcinoma. Cases of Hürthle cell carcinoma showed the longest median survival. There was no significant difference in survival among patients up to or older than 45 years at the time of metastases (P =.31). CONCLUSIONS Most thyroid carcinomas with bone metastases are of papillary type, and most have poorly differentiated or undifferentiated features. The influence of the microscopic tumor type and tumor differentiation on survival after bone metastasis primarily appears to be due to the much worse prognosis among anaplastic and medullary carcinomas. Age at diagnosis of bone metastases does not influence survivals.