Primary pure signet-ring cell carcinoma of the extrapulmonary left main bronchus: a case report with an immunohistochemical study

Although several case reports and series of primary signet-ring cell adenocarcinoma (SRCA) of the lung have been reported, primary SRCA of the extrapulmonary main bronchus has not been reported. A 61-year-old man was found to have a tumor of the mediastinum of the left pulmonary hilus on routine chest X-ray examination. A transbronchial endoscopy revealed an elevated tumor in the extrapulmonary left bronchus near the tracheal bifurcation. Biopsy was taken from the bronchial lesion. It revealed pure typical SRCA. Histochemically, Alcian-blue/PAS stain showed intracytoplasmic mucins. Immunohistochemically, the tumor cells were positive for cytokeratin (CK) AE1/3, CK CAM5.2, CK7, CK18, CEA, EMA, CA19-9, Ki-67 (labeling=20%), p53, and MUC1. They were negative for CK34BE12, CK5/6, CK8, CK14, CK19, CK20, p63, vimentin, TTF-1, CDX-2, MUC2, MUC5AC and MUC6. The pathological diagnosis of primary SRCA of the left main bronchus was made. The patient died of carcinomatosis 18 months after the first presentation. In conclusion, the author reported the first case of primary SRCA of the extrapulmonary left main bronchus near the tracheal bifurcation with an extensive immunohistochemical study.