Leukemia is a type of cancer that affects the blood and bone marrow. It occurs when the body produces an excessive number of abnormal white blood cells, which can interfere with the body's ability to fight infections. There are different types of leukemia, including acute lymphoblastic leukemia and chronic myeloid leukemia, each with its own characteristics and treatment options. Symptoms of leukemia can include fatigue, frequent infections, easy bruising, and unexplained weight loss. Diagnosis typically involves blood tests and bone marrow examinations. Treatment may include chemotherapy, radiation therapy, or even a stem cell transplant to help restore healthy blood cells.