Abstract Cancer cells are surrounded by a fluid-mosaic membrane that provides a highly dynamic structural barrier with the microenvironment, communication filter and transport, receptor and enzyme platform. This structure forms because of the physical properties of its constituents, which can move laterally and selectively within the membrane plane and associate with similar or different constituents, forming specific, functional domains. Over the years, data have accumulated on the amounts, structures, and mobilities of membrane constituents after transformation and during progression and metastasis. More recent information has shown the importance of specialized membrane domains, such as lipid rafts, protein-lipid complexes, receptor complexes, invadopodia, and other cellular structures in the malignant process. In describing the mac-rostructure and dynamics of plasma membranes, membrane-associated cytoskeletal structures and extracellular matrix are also important, constraining the motion of membrane components and acting as traction points for cell motility. These associations may be altered in malignant cells, and probably also in surrounding normal cells, promoting invasion and metastatic colonization. In addition, components can be released from cells as secretory molecules, enzymes, receptors, large macromolecular complexes, membrane vesicles, and exo-somes that can modify the microenvironment, provide specific cross-talk, and facilitate invasion, survival, and growth of malignant cells. Introduction Cell membranes represent important cellular barriers and first-contact structures of normal and cancer cells. Extracellular signals from ions, hormones, cytokines, enzymes, growth and motility factors, receptors, extracellular matrix (ECM), other stromal elements, and subcellular membrane vesicles must first interact with the cell membrane to initiate signaling processes. Therefore, cell or plasma membranes are cellular filters that can selectively transmit signals and substances from outside cells and from adjacent cells into a cell's interior. Conversely, they can also release signals and molecules to other cells and the micro- and macro-environment in a complex process that has been termed "social cell biology" (1). In addition, cells are compartmentalized into organelles by various intracellular membrane structures that are responsible for biosynthesis, energy production, replication, transportation, recycling, destruction, secretion, and other cellular activities.
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