Histopathologic characterization of radioactive iodine‐refractory fluorodeoxyglucose‐positron emission tomography‐positive thyroid carcinoma

• Published in: Cancer 2008-07, Vol.113 (1), p.48-56
• Main Authors: Rivera, Michael, Ghossein, Ronald A., Schoder, Heiko, Gomez, Daniel, Larson, Steven M., Tuttle, R. Michael
• Format: Article
• Language: English
• Subjects: Adult; Aged; Biological and medical sciences; Disease-Free Survival; Endocrinopathies; Female; Fluorodeoxyglucose F18; fluorodeoxyglucose‐positron emission tomography (FDG‐PET); histopathologic characterization; Humans; Iodine Radioisotopes; Male; Malignant tumors; Medical sciences; Middle Aged; Neoplasm Metastasis; Neoplasm Recurrence, Local; Positron-Emission Tomography; radioactive iodine; Radiopharmaceuticals; Survival Analysis; thyroid carcinoma; Thyroid Neoplasms - pathology; Thyroid. Thyroid axis (diseases); Tumors
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/cncr.23515

BACKGROUND. Radioactive iodine‐refractory (RAIR) 18F‐fluorodeoxyglucose (FDG)‐positron emission tomography (PET) positive thyroid carcinomas represent the major cause of deaths from thyroid carcinomas (TC) and are therefore the main focus of novel target therapies. However, to the authors' knowledge, the histology of FDG‐PET‐positive RAIR metastatic thyroid carcinoma has not been described to date. METHODS. Metastatic tissue from RAIR PET‐positive patients identified between 1996 and 2003 at the study institution were selected for histologic examination. The biopsied metastatic site corresponded to a FDG‐PET positive lesion sampled within 2 years (87% of which were sampled within 1 year) of the PET scan. Detailed microscopic examination was performed on the metastatic deposit and the available primary tumors. Poorly differentiated thyroid carcinomas (PDTC) were defined on the basis of high mitotic activity (≥5 mitoses/10 high‐power fields) and/or tumor necrosis. Other types of carcinomas were defined by conventional criteria. The histology of the metastases and primary were analyzed, with disease‐specific survival (DSS) as the endpoint. RESULTS. A total of 70 patients satisfied the selection criteria, 43 of whom had primary tumors available for review. Histologic characterization of the metastasis/recurrence in 70 patients revealed that 47.1% (n = 33 patients) had PDTC, 20% (n = 14 patients) had the tall cell variant (TCV) of papillary thyroid carcinoma, 22.9% (n = 16 patients) had well‐differentiated papillary thyroid carcinoma (WDPTC), 8.6% (n = 6 patients) had Hurthle cell carcinoma (HCC), and 1.4% (n = 1 patient) had anaplastic carcinomas. The histopathologic distribution of the tumor in the primaries was: PDTC, 51%; TCV, 19%; WDPTC, 23%; and widely invasive HCC, 7%. A differing histology between the primary tumor and metastasis was observed in 37% of cases (n = 16 patients). In the majority of instances (63%; 10 of 16 patients) this was noted as transformation to a higher grade. Of the primary tumors classified as PTC, 70% progressed to more aggressive histotypes in the metastasis. Tumor necrosis and extensive extrathyroid extension in the primary tumor were found to be independent predictors of poorer DSS in this group of patients (P = .015). Approximately 68% of the PDTC primary tumors were initially classified by the primary pathologist as better‐differentiated tumors on the basis of the presence of papillary and/or follicular architecture or the p