A 42-year-old woman, who had received right breast-conserving therapy 5 years previously, was admitted with hemoptysis. Chest X-rays showed a tumor shadow in the left pulmonary hilus with partial atelectasis in the left lower lobe. Bronchofiberscopic examination showed a polypoid tumor arising from the endobronchial wall, with bleeding and a white surface coat. Although, microscopically, the tumor resembled the breast cancer resected previously, as we could not rule out primary lung carcinoma, and as the tumor seemed to be localized, thoracotomy was performed. During posterolateral thoracotomy, however, pleural metastatic nodules were found; therefore, only sampling of these nodules and the administration of 50 mg of cisplatin (CDDP) into the thoracic cavity were performed. From a comparison of the histopathological features of the original tumor and the intrathoracic tumor, and from the hormone receptor positivity of the pleural metastasis, we diagnosed the intrathoracic tumor as being highly suspicious of metastasis from breast cancer. The measurement of hormone receptor was informative for the diagnosis of and for selecting a therapeutic strategy for the metastatic breast cancer.