Pulmonary adenocarcinoma with osseous metaplasia: a rare occurrence possibly associated with early stage?
A 60-year-old Chinese woman presented with the symptom of bloody sputum, which she had noticed for 2 weeks. Enhanced computed tomography (CT) showed an irregular abnormal soft tissue mass located in the left upper lobe that was approximately 1.7 cm× 0.8 cm in size and obviously enhanced with contrast medium (). The CT value in the enhanced arterial phase was approximately 40–60 Hounsfield units, while the venous phase CT value was approximately 72 Hounsfield units. Minimal calcification was not apparent in the tumor. The patient denied any history of gastric carcinoma or digestive symptoms. On the basis of her history and imaging studies, the patient was diagnosed with a malignant pulmonary tumor and underwent lobectomy. The tumor had a heterogeneous off-white appearance and was solid with unclear boundaries. No depressions or varicose veins were found in the pleura.\nHematoxylin and eosin-stained sections showed that the alveolar structure had disappeared within the tumor and that the tumor cells were distributed into round or oval glands with a central lumen. There was no mucin in the tumor cell cytoplasm or glandular cavity. The tumor cell nuclei were ovoid and dark-stained, with prominent nucleoli. The mitotic activity was approximately two mitoses per ten high-powered fields. New bone formation was observed at the center of the tumor (approximately 1.25 mm × 0.85 mm, ). The bone island consisted of mature bone tissue and was surrounded by osteoblast cells that were accompanied by proliferating fibroblasts (). No bone marrow cells were present in the bone tissue. Immunohistochemical staining showed that the tumor cells were positive for cytokeratin-7 () and thyroid transcription factor-1 (), but the metaplastic bone tissue was negative for these factors. However, the tumor cells were negative for caudal-related homeodomain protein 2, which ruled out the possibility of gastrointestinal adenocarcinoma metastasis to the lung, and the Ki-67 labeling index was approximately 35%. An epidermal growth factor receptor exon 19 deletion mutation was found in this patient, but the echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase rearrangement was not found. On the basis of histologic and immunohistochemical findings, this tumor was diagnosed as an invasive pulmonary adenocarcinoma with a predominant acinar pattern, accompanied by osseous metaplasia in tiny lesions and without lymphatic metastasis. This diagnosis was based on the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification system for standard lung adenocarcinoma.