A third group of genes in which mutations lead to a significant susceptibility to cancer is the class of landscaper genes.  Products encoded by landscaper genes do not directly affect cellular growth, but when mutated, contribute to the neoplastic growth of cells by fostering stromal environments conducive to unregulated cell proliferation.
Landscaper genes encode gene products that control the microenvironment in which cells grow.  Growth of cells depends both on cell-to-cell interactions and cell-to-extracellular matrix (ECM) interactions.  Mechanisms of control via regulation of extracellular matrix proteins, cellular surface markers, cellular adhesion molecules, and growth factors have been proposed.
Cells communicate with each other via the ECM through both direct contact and through signaling molecules.  Stromal cell abnormalities arising from gene products coded by faulty landscaper genes could induce abnormal cell growth on the epithelium, leading to cancer of that tissue.
Biochemical cascades consisting of signaling proteins occur in the ECM and play an important role to the regulation of many aspects of cell life.  Landscaper genes encode products that determine the composition of the membranes in which cells live.  For example, large molecular weight glycoproteins and proteoglycans have been found to in association with signaling and structural roles.  There exist proteolytic molecules in the ECM that are essential for clearing unwanted molecules, such as growth factors, cell adhesion molecules, and others from the space surrounding cells.  It is proposed that landscaper genes control the mechanisms by which these factors are properly cleared.  Different characteristics of these membranes lead to different cellular effects, such as differing rates of cell proliferation or differentiation.  If, for example, the ECM is disrupted, incoming cells, such as those of the immune system, can overload the area and release chemical signals that induce abnormal cell proliferation.  These conditions lead to an environment conducive to tumor growth and the cancerous phenotype.