Cancer cells can spread to other parts of the body through the blood and lymph systems; when this occurs, the cancer has metastasized.  The property of cancer cells to invade and colonize other tissues is called metastasis.

In most human cancer, it is not the primary tumour that causes the death of the patient, but instead a subsequent tumour that often grows at a different site (secondary, tertiary, etc. tumours).

To obtain the best prognosis, a cancer must be diagnosed at early stages, when the cancer has not metastasized.

If a cancer originated in the lung and has metastasized to the brain, it is still a lung cancer; it remains named from the primary site in the cancer. When cancer cells metastasize and cause secondary tumours, the cells in the metastatic tumour do not have the properties of the cells from the tissue they invade, but are similar to those found in the original organ.

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