Leukemia is a serious disease where the body produces too many abnormal white blood cells that don't work properly. White blood cells normally help fight infections, but in leukemia, defective cells multiply out of control and crowd out the healthy blood cells a person needs to stay well.

Leukemia is a type of cancer that affects the bone marrow, the spongy tissue inside bones where blood cells are made.

Different types of leukemia affect people differently. Some develop quickly and need immediate treatment, while others progress more slowly. Treatments have improved dramatically over the past few decades: doctors use chemotherapy, radiation, and sometimes bone marrow transplants to fight the disease. Many people, especially children, recover completely from leukemia thanks to modern medicine.

When someone has leukemia, they may feel extremely tired, get infections easily, and bruise without much reason because their blood isn't working as it should. While leukemia is frightening, medical researchers continue making progress, and survival rates keep improving as scientists learn more about how to treat it effectively.