[428] Diagnostic Value of Thyroid Transcription Factor-1 and Thyroglobulin in Differentiating Thyroid Carcinoma and Adenocarcinoma of the Lung

Srividya Sathiyamoorthy, Zahra Maleki. Johns Hopkins Hospital, Baltimore, MD

Background: Thyroid carcinomas and adenocarcinomas of the lung may share cytomorphological features while having vastly different clinical management. Occasionally, lung adenocarcinomas metastasizing to the thyroid or thyroid carcinomas metastasizing to the lung can be the initial presentation of these carcinomas. Thyroid Transcription Factor-1 (TTF-1) is routinely used to detect metastases of pulmonary adenocarcinomas and TTF-1 and Thyroglobulin (TGB) together are used to detect carcinomas of thyroid origin. We demonstrate the diagnostic value of TTF-1/TGB together to avoid misdiagnoses of thyroid carcinomas and lung adenocarcinomas.
Design: The cytopathology archives of a tertiary care center were retrospectively searched over a 10-year period (2001-2011) for cases of adenocarcinoma of lung versus thyroid. TTF-1 and TGB IHC were performed on all these cases. TTF-1 and TGB expression were reviewed and the data analyzed.
Results: Forty four cases of adenocarcinoma were found, that were worked up for adenocarcinoma of lung versus thyroid. The anatomic locations were: bone (4), liver (3), lung (5), lymph nodes (11-axillary-1, cervical-2, mediastinal-3, supraclavicular-3, subclavilar-1, not specified-1), neck (4), pleural fluid (8), soft tissue (4), and thyroid (4). Twenty six cases expressed TTF-1, but were negative for TGB. Twenty five of these cases were diagnosed as metastatic adenocarcinoma consistent with (c/w) a lung primary, two of which were in the thyroid and 1 case as adenocarcinoma of lung. Sixteen cases expressed both TTF-1 and TGB and were diagnosed as metastatic thyroid malignancies. Twelve of these were metastatic papillary thyroid carcinoma (PTC), one PTC, one metastatic follicular carcinoma and one poorly differentiated thyroid carcinoma. Three of these were metastatic PTC to the lung. Three cases were diagnosed as metastatic PTC, PTC and anaplastic thyroid carcinoma, while expressing TGB and being negative for TTF-1.
Conclusions: The clinical management of metastatic lung adenocarcinoma and metastatic thyroid carcinoma differ vastly. Among the cases in our study, two were those of adenocarcinoma of lung metastatic to thyroid and 3 cases were metastatic PTC to lung. While TTF-1 can be expressed in both lung and thyroid malignancies, TGB can be used as a differential marker. Having a high index of suspicion for metastatic lesions in cases that appear to be straightforward cases of primary lung or thyroid carcinomas will prompt the pathologist to evaluate these lesions for the expression of both TTF-1 and TGB so as to prevent misdiagnoses.
Category: Cytopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 72, Wednesday Afternoon

 

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