Metastasis is the multi step process by which cancer cells spread from a primary tumor to distant organs and is responsible for most cancer related deaths. Research shows that this is not a random event but a highly regulated biological cascade shaped by both cancer cells and their microenvironment.

To metastasize, tumor cells must first acquire motility and invasive capacity, often through epithelial to mesenchymal transition, which reduces cell adhesion and increases plasticity. They degrade the surrounding extracellular matrix using enzymes such as matrix metalloproteinases and intravasate into blood or lymphatic vessels. Circulating tumor cells must then survive mechanical stress and immune attack in the bloodstream, often by forming clusters or interacting with platelets.

At distant sites, cells leave the circulation and enter new tissues. Organ specificity arises from compatibility between tumor cell traits and the molecular and structural features of target organs. Before cancer cells arrive, primary tumors can condition distant tissues by releasing soluble factors and extracellular vesicles that remodel local immunity and vasculature, creating a pre metastatic niche.

Within metastatic sites, most disseminated cells either die or enter dormancy. A minority adapt to the new microenvironment through metabolic rewiring, interaction with stromal cells and evasion of local immune surveillance, eventually forming clinically detectable lesions.

Current research highlights metastasis as a reversible, dynamic process involving phenotypic plasticity, immune modulation and bidirectional communication between tumor and host tissues. Therapeutic strategies are shifting toward targeting early dissemination, circulating tumor cells, pre metastatic niche formation and the survival of dormant cells, in addition to controlling established metastases.