Bronchioloalveolar carcinoma (BAC) has features distinct from those of conventional pulmonary
adenocarcinoma (CPA) in terms of its characteristic growth pattern along alveolar walls and intrapulmonary
metastasis via the aerogenous route. We speculated, therefore, that BAC might differ from CPA in its capacity for cell-to-cell or cell-to-basement membrane adhesion.
E-cadherin (E-CD), one of the most important elements of epithelial integrity molecules, is related to
tumor metastasis in various organs. Differences of E-CD and associated
catenin expressions between BAC and CPA, however, have not been elucidated. We examined the expression of E-CD and alpha-, beta- and
gamma-catenin immunohistochemically in 18 BACs (9 mucinous, 7 nonmucinous, and 2 sclerosing) in comparison with CPAs, all of which were well-differentiated
adenocarcinomas. In addition, we analyzed the correlation between the expression of these
cell adhesion molecules and the presence of intrapulmonary
metastasis, histologic subtypes, and cell proliferation activity. Clinicopathologically, we observed intrapulmonary
metastases in 4 of the 18 BACs and none of the CPAs. In 14 of the 18 BACs, more than one-half of the
tumor cells expressed E-CD, and the E-CD expression level was significantly higher in the BACs than in the CPAs. In addition, all of the BACs exhibited preserved membranous staining for E-CD, whereas in 5 of the 14 CPAs, the expression pattern was disorganized cytoplasmic staining; the difference was statistically significant. The Ki-67 labeling index was significantly lower in the BACs than in the CPAs. There were no appreciable differences in E-CD expression among the BAC subtypes. E-CD expression was significantly lower in the BACs with intrapulmonary
metastasis than in the BACs without intrapulmonary
metastasis. These findings indicated to us that BAC was distinct from CPA in terms of proliferation activity and expression of certain adhesion molecules and that E-CD downregulation was associated with a tendency toward intrapulmonary
metastasis.