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Secondary lung cancer. Light micrograph of a section through lung tissue showing cancer cells (with dark, irregular nuclei) due to the spread of cancer from the liver. The spread of a cancer from one site in the body to others is called metastasis. Once a cancer has spread throughout the body, any treatment must be systemic. Removal of all tumours must be followed by chemo- and radiotherapy (drug and radiation treatment). The prognosis is poor for most systemic cancer. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/CNRI)