Blood cancers affect blood cells and bone marrow - the spongy tissue inside your bones where blood cells are made. These cancers change the way blood cells behave and how well they work. You have three types of blood cells: White blood cells fight infection as part of your immune system. Red blood cells carry oxygen to your body's tissues and organs and bring carbon dioxide to your lungs so you can breathe it out. Platelets help your blood clot when you're injured. There are three major types of blood cancer: Leukemia Lymphoma Myeloma These cancers cause your bone marrow and lymphatic system to make blood cells that don't work as well as they should. They all affect different types of white blood cells, and they act in different ways.