Composite coloured positron emission tomography (PET) and computed tomography (CT) scans of the chest of a 57 year old woman with metastatic breast cancer. The scan at left shows a cancer (bright yellow at upper left of scan) that has metastasised (spread) to the right serratus anterior muscle from a primary cancer of the right breast that has been surgically removed. The scan at right was taken after surgery to remove the metastatic tumour.