Primary enteric adenocarcinoma with predominantly signet ring features of the lung: A case report with clinicopathological and molecular findings

Primary signet ring adenocarcinoma (SRA) of the lung is a rare condition. An 81-year-old man was referred to our hospital because of bloody sputum. Chest radiography showed a tumor in the right lung and biopsies revealed typical SRA. No tumors except for the one in the right lung were found. Therefore, diagnosis of primary lung SRA was made. The SRA cells showed intracytoplasmic mucin that were characterized by crescentic nuclei displaced toward one end of the cell. The tumor cells showed negative immunostaining for thyroid transcription factor 1 (TTF-1), but positive immunostaining for CDX2, cytokeratin-20 (CK20), Ki-67 (labeling = 50%), p53, and focally CK7. A right lower lobectomy and lymph node dissection were performed via video-assisted thoracic surgery. After surgery, uracil-tegafur (184 mg/m 2 /day) was administered for five days, followed by a 2-day rest period for a duration of two years in total. No recurrence was observed during the monthly-follow ups, and the patient did not experience any complications. In conclusion, we describe an extremely rare case of primary enteric adenocarcinoma with predominantly signet ring features of the lung. Our case report includes in-depth immunohistochemical and molecular data.