A metastasis is the spread of tumour cells from the place where the tumour started to a different part of the body. Tumour cells can travel to a lymph node or to another organ such as the lungs, liver, bones, or brain.
When performing surgery to remove a tumour, lymph nodes in the areas of a tumour are often also removed. A pathologist then examines the lymph nodes under a microscope to look for cancer cells.
A small sample of tissue can also be removed from an organ such as the lungs or liver to look for cancer cells that may have traveled there from a tumour in a different part of the body.
The ability to metastasize is usually associated with cancers, however, there are some non-cancerous tumours that are also known to metastasize.
For many types of cancers, the patient is harmed more by the metastatic disease than by the primary tumour (which can often be removed surgically). In addition, some types of cancer are much more likely to metastasize to lymph nodes while others metastasize to distant organs.
Why is this important? For most types of cancers, metastatic disease is used to determine the pathologic stage. Cancer cells found in a lymph node or distant organ are often associated with a higher stage and worse prognosis.