Our findings that CDH1/E-cad expression is not significantly downregulated when primary tumors progress into metastatic tumors (Fig. 6), which are consistent with the observations from other groups [13, 20, 28, 29], suggest that single-cell invasion/migration may not be the preferred mode of invasion/migration, and collective invasion/migration might be the predominant form of invasion/migration for most carcinomas, a notion that is supported by several studies monitoring metastatic tumors in circulation [81, 87, 88]. The gene discussed is CDH1; the disease is carcinoma.