Spread of cancer cells beyond the tissue where they originated is called

Metastasis 
The main reason that cancer is so serious is its ability to spread in the body. Cancer cells can spread locally by moving into nearby normal tissue. Cancer can also spread regionally, to nearby lymph nodes, tissues, or organs. And it can spread to distant parts of the body. When this happens, it is called metastatic cancer. For many types of cancer, it is also called stage IV cancer. The process by which cancer cells spread to other parts of the body is called metastasis.