A Rare Case of Tumor-to-Tumor Metastasis of Thyroid Papillary Carcinoma within a Pulmonary Adenocarcinoma

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Tumor-to-tumor metastasis (TTM) is a rare phenomenon first reported several decades ago in Fried's description of a broncho-genic carcinoma that metastasized to a meningioma. 1 According to previous studies, renal cell carcinoma and meningioma are common recipients, whereas lung and breast cancer are common donors. 2 Thus far, four cases of lung carcinoma harboring papillary thyroid carcinoma (PTC) metastasis have been reported in the English literature. 3-6 Here we present another case of PTC that metastasized to pulmonary adenocarcinoma. A 56-year-old non-smoking male presented with a 3-month history of cough and sputum. On chest computed tomography, a 53-mm-sized ground-glass opacity in the left upper lobe (LUL) of the lung was identified (Fig. 1A left). On positron emission tomography, F-18 fluorodeoxyglucose uptake was detected in the left thyroid accompanied by lymphadenopathy (Fig. 1A right). Histological confirmation was performed for each lesion. Fine needle aspiration of thyroid and bronchoscopic biopsy of the lung lesion revealed PTC with cervical lymph node metastasis and pulmonary adenocarcinoma, respectively. Lobectomy of the LUL was performed prior to thyroid cancer treatment. A single, well-defined, 0.6×0.6-cm-sized, round, firm, white-tan nodule was found in the peribronchial area within a 3.9×3.1-cm-sized, irregular, soft, grey mass in the anterior segment of the LUL, on gross examination (Fig. 1B) and low-power magnification (Fig. 1C). No other suspicious lesions were detected in the given specimen. The main lung lesion was diagnosed as conventional pulmonary adenocarcinoma and was composed of moderately differentiated adenocarcinoma with an acinar and papillary pattern accompanied by a focal micropapillary pattern (Fig. 1D). The small nodule within the adenocarcinoma (Fig. 1D) was comprised of papillae lined by cuboidal cells with nuclear clearing and grooves suggestive of PTC (Fig. 1E). Additional thyroglobulin immunohistochemical staining (1:1,000, Dako, Glostrup, Denmark) highlighted metastatic PTCs in a total of three foci (Fig. 1F). A metastatic papillary carcinoma was also identified in a separately submitted mediastinal lymph node. Subsequent total thyroidectomy with central neck node dis-section was performed one month after lobectomy. Bilateral PTCs (3.3×3 cm and 0.3×0.3 cm) and metastasis to 17 of 36 regional lymph nodes were identified on histologic examination. DISCUSSION Synchronous primary cancers are occasionally observed, but TTM is extremely rare; only about 100 cases …