Hippocrates (a very famous ancient doctor who is often called the father of modern medicine) named many kinds of cancer. He called benign tumours (tumors that are not made up of cancer cells) "oncos". In Greek, "onkos" means 'swelling'. He called malignant tumours "karkinos". This means crab or crayfish in Greek. He used this term because he thought that if a solid malignant tumor was cut into, its veins looked like a crab: "the veins stretched on all sides as the animal the crab has its feet, whence it derives (gets) its name". Hippocrates later added "-oma" (Greek for 'swelling') after the word 'carcinos'. This is how the word "carcinoma" came about.