[Lung non-terminal respiratory unit type adenocarcinoma: a clinicopathologic study]

Objective: To evaluate the clinicopathologic characteristics of lung non-terminal respiratory unit (non-TRU) type adenocarcinoma. Methods: Seventy-two cases of lung non-TRU type adenocarcinoma that underwent complete resection and diagnosed at Departments of Pathology, Affiliated Suzhou Hospital of Nanjing Medical University and Nanjing General Hospital of the PLA from January 2005 to December 2016 were retrospectively studied. The histomorphological changes and precursor lesions were observed under microscope. The expression of lineage-specific markers and tumor stem cell markers was detected by immunohistochemistry (IHC). The major driver mutations of lung adenocarcinoma were tested by ARMS and directive gene sequencing. Results: Non-TRU type adenocarcinomas were more commonly found in male (65.3%, 47/72), former or current smokers (68.1%, 49/72), the elder (mean 61 years old), central adenocarcinoma (75.0%, 54/72), tumors with necrosis (61.1%, 44/72) and higher grade (73.6%, 53/72). Histologically, non-TRU type adenocarcinoma displayed complex histomorphology and was often composed of large irregular gland-like and acinar pattern accumulating extracellular mucin, necrotic tumor cell debris and neutrophils, or invasive adenocarcinoma with mucin production. The tumor cells were composed of bronchial surface epithelial cells, mucinous column cells, polygonal cells and goblet cells. Eighteen (25.0%), 23 (31.9%) and 28 (38.9%) cases exhibited ciliated columnar cell metaplasia (CCCM), mucous columnar cell change (MCCC) and bronchiolar columnar cell dysplasia (BCCD) (precursor lesion of lung adenocarcinoma). IHC showed the expression of CK7 (100.0%, 72/72), TTF1 (12.5%, 9/72), Napsin A (5.6%, 4/72), MUC5AC (81.9%, 59/72), MUC5B (87.5%, 63/72), p53 (66.7%, 48/72), CK5/6 (12.5%, 9/72), p63 (18.1%, 13/72), CK20 (19.4%, 14/72) and CDX2 (16.7%, 12/72) in the tumor cells. The expression of tumor stem cell markers was detected in 43.1% cases (31/72) for CD44, 31.9% (23/72) for CD133, 58.3% (42/72) for β-catenin, 36.1% (26/72) for ALDH1, 12.5% (9/72) for GATA6, 20.8% (15/72) for SOX2 and 29.2% (21/72) for OCT4. The driver mutations were 26.4% (19/72) for KRAS, 2.8% (2/72) for EGFR and 1.4% (1/72) for EML4-ALK, and none for BRAF and ROS1. Conclusion: Non-TRU type adenocarcinoma is an uncommon subtype of lung adenocarcinoma with distinct clinicopathologic characteristics, histologic appearances, immunophenotype and molecular genetic alterations.