Laminins are structural components of the basement membrane and play a key role in cell adhesion, migration, differentiation and proliferation of several cell types. They also act as barriers to the passage of cells (with the exceptions of macrophages and lymphocytes) and form a continuous sheet around epithelial structures. Laminin itself can serve as an effective barrier for non-invasive cells and is employed in various types of cell-based assays. The basement membrane is compromised by tumor cells during invasion and metastasis when the laminin layer is degraded and penetrated.