The histologic distinction between bronchioloalveolar carcinoma and other adenocarcinomas is tissue invasion. The clinical importance of lung adenocarcinoma invasion is supported by several recent studies indicating that the risk of death in nonmucinous bronchioloalveolar carcinoma is significantly lower than that of pure invasive tumors and in tumors with greater than 0.5 cm of fibrosis or linear invasion. Using microarray gene expression profiling of human tumors, dysregulation of transforming growth factor-² signaling was identified as an important mediator of tumor invasion.
