Metastatic thoracic lymph node carcinoma of unknown origin on which we performed two kinds of immunohistochemical examinations.

Metastatic cancers of the thoracic lymph nodes without primary sites are rare. Such cancers are difficult for clinicians to manage as identifying the primary sites is difficult in using routine histologic examinations alone. We searched for the site of the primary lesion using immunohistochemical exploration of cytokeratin (CK) and thyroid transcription factors 1 (TTF-1), and 2-[18F] and fluorodeoxyglucose positron emission tomography (FDG PET) in a patient with cancer of the hilar lymph node without any known primary site. To our knowledge, there are no previous similar reports. A 45-year-old man presenting with a tumor in the right hilar region, underwent surgical resection of the tumor, resulting in a diagnosis of metastatic cancer of the bronchopulmonary lymph nodes. An immunohistochemical examination revealed the neoplastic lesion to be positive for CK7, negative for CK20, and negative for TTF-1. Repeated searches to identify the site of the primary lesion by FDG PET over the 35 months since operation have failed to locate a primary site.