Acute lymphoblastic leukemia (ALL) is a type of cancer that affects the blood and bone marrow. It occurs when the body produces an excessive number of immature white blood cells, known as lymphoblasts. These abnormal cells crowd out healthy blood cells, leading to symptoms such as fatigue, frequent infections, and easy bruising or bleeding. ALL is most commonly diagnosed in children, but it can also occur in adults. Treatment typically involves chemotherapy, which aims to kill the cancerous cells and restore normal blood cell production. In some cases, a stem cell transplant may be necessary to achieve remission.