How do malignant tumors invade nearby tissues?

Malignant tumors invade nearby tissues through a complex, multi-step process that begins with the loss of normal cellular cohesion. Typically, cells are held together by specialized molecules like E-cadherin; however, cancer cells often reduce the expression of these adhesion molecules, allowing them to detach from the primary tumor mass.12

To breach the basement membrane—a structural barrier between tissues—tumor cells exploit biological programs such as the "epithelial-mesenchymal transition." During this process, cells become more mobile and elongated. They forge a path through the extracellular matrix by secreting enzymes that digest surrounding tissue or by stimulating nearby stromal cells to do so.12

Furthermore, tumor cells avoid apoptosis, which would normally trigger cell death if a cell detached from its matrix. Once they have successfully breached the basement membrane, these cells can infiltrate surrounding tissues and gain access to lymphatic or blood vessels, facilitating their spread to distant sites in the body. This invasive capacity is often further supported by interactions with host immune system cells and connective tissue cells at the tumor edge.231