[Occult Thyroid Cancer Diagnosed by Metastasis to an Upper Mediastinal Lymph Node Removed during Surgery for Primary Lung Cancer].

A computed tomography (CT) scan revealed 2 nodules in the right upper and middle lobes of the lung and swelling of an upper mediastinal lymph node (#2R) in a 77-year-old male. Positron emission tomography (PET)/CT showed abnormal uptake only in the right middle lobe nodule, so we suspected a double primary lung cancer (cT1bN0M0, stage ⅠA), and performed a right upper and middle lobectomy with ND2a-2 dissection. Pathological investigation revealed that the lung nodules were adenocarcinomas and the lymph node swelling #2R was a metastasis of thyroid cancer. After surgery, careful examination was done for thyroid but the primary lesion was not found. Careful observation for an occult thyroid cancer is continuing at the outpatient.