<unk>  is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to<unk>  by a cancerous tumor. The newly pathological sites, then, are<unk>  <unk> s). It is generally distinguished from cancer invasion, which is the direct extension and penetration by cancer cells into neighboring tissues. Cancer occurs after cells are genetically altered to proliferate rapidly and indefinitely. This uncontrolled proliferation by mitosis produces a primary heterogeneic tumour. The cells which constitute the tumor eventually undergo<unk> aplasia, followed by dysplasia then anaplasia, resulting in a malignant phenotype. This malignancy allows for invasion into the circulation, followed by invasion to a second site for tumorigenesis. Some cancer cells known as circulating tumor cells acquire the ability to penetrate the walls of lymphatic or blood vessels, after which they are able to circulate through the bloodstream to other sites and tissues in the body. This process is known (respectively) as lymphatic or hematogenous spread. After the tumor cells come to rest at another site, they re-penetrate the vessel or walls and continue to multiply, eventually forming another clinically detectable tumor. This new tumor is known as a<unk> astatic (or secondary) tumor.<unk>  is one of the hallmarks of cancer, distinguishing it from benign tumors. Most cancers can<unk> e, although in varying degrees. Basal cell carcinoma for example rarely<unk> es. When tumor cells<unk> e, the new tumor is called a secondary or<unk> astatic tumor, and its cells are similar to those in the original or primary tumor. This means that if breast cancer<unk> es to the lungs, the secondary tumor is made up of abnormal breast cells, not of abnormal lung cells. The tumor in the lung is then called<unk> astatic breast cancer, not lung cancer.<unk>  is a key element in cancer staging systems such as the TNM staging system, where it represents the "M". In overall stage grouping,<unk>  places a cancer in Stage IV. The possibilities of curative treatment are greatly reduced, or often entirely removed when a cancer has<unk> ed.
Metastasis
Diastasis 
Gliosis
Mixed tumor
Stoma 
Lymphatogenous metastasis
Vascular tumor
Tumor progression