Thyroid metastasis of pulmonary adenocarcinoma with EGFR G719A mutation: Genetic confirmation with liquid-based cytology specimens.

Lung cancer is one of the most common cancers worldwide, and frequently metastasizes to other organs such as the lymph nodes, brain, and bone; metastasis of lung cancer to the thyroid, however, is rare 1 . Primary thyroid cancer, in contrast, is less common, yet the lung is one of its most common sites of distant metastasis 2 . In any patient with both lung and thyroid tumors, therefore, we must obtain conclusive, ideally genetic, evidence, if we are to reach a conclusive diagnosis, especially when the lung cancer is adenocarcinoma, whose pathological features partly overlap with those of papillary thyroid carcinoma (PTC), the most common form of thyroid cancer. Here, we report an elderly woman with pulmonary adenocarcinoma with thyroid metastasis, which we confirmed by genetic analysis using liquid-based cytology (LBC) material from both lung and thyroid tumors.