Lung cancer with breast metastasis: a case report and review of the literature.

In this article, we present a rare case of breast metastasis of lung cancer. Chest computed tomography (CT) for a woman in her early 50s indicated right lung malignancy, multiple bone metastases, and an irregular mass in her right breast. Further inquiry into the case history revealed that the patient had been aware of the breast mass for 3 years, without respiratory symptoms. Biopsy of the breast mass suggested estrogen receptor (ER) (+), progesterone receptor (PR) (-), and human epidermal growth factor receptor 2 (HER2) (+ +) breast cancer. The patient was initially diagnosed with breast cancer with lung and bone metastasis. However, comprehensive breast cancer treatment was ineffective, and thyroid transcription factor-1 (TTF-1), napsin A, and cytokeratin 7 (CK7) were evaluated to better understand the origin of the cancer. To the best of our knowledge, this patient had the longest reported disease course from presentation with a breast lump as the first symptom to the final diagnosis of breast metastasis of lung cancer. To provide a better reference for differential diagnosis of ambiguous tumors, we also performed a systematic literature review.