What is Acute Lymphoblastic Leukemia?

Leukaemia or blood cancer is the cancer of the white blood cells. In acute leukemia the condition progresses rapidly unlike in chronic leukemia. Leukemia is divided into four major types:-

• Acute myeloid leukemia (AML)
• Chronic myeloid leukemia (CML)
• Acute lymphoblastic leukemia (ALL)
• Chronic lymphoblastic leukemia (CLL)

This article focuses on the Acute lymphoblastic leukemia (ALL) type of leukemia.

What happens in ALL?

Normally the blood cells are produced by bone marrow. Bone marrow is a spongy material found inside the bones. There are stem cells within the bone marrow that mature to form the blood cells. Stem cells have the ability to create other specialised cells.

These stem cells are responsible for creation of:

• red blood cells that help carry oxygen to various parts of the body
• white blood cells that form the immune system and fight off invading microbes
• platelets that help in clotting and prevention of bleeding

The bone marrow produces mature forms of each of these types of cells. In leukemia, the affected bone marrow fails to release adult and mature cells and releases a large number of immature white blood cells that are known as blast cells.

These blast cells disrupt the normal balance of cells in the blood leading to shortage of red blood cells causing anemia and platelets causing bleeding tendencies. Shortage of adult and mature white blood cells means an increased risk of infections as well.

In ALL the lymphoid cells of the white blood cells are affected. These include the lymphocytes of the white blood cells. There is a cancerous transformation of a clone of cells from lymphoid progenitor cells. These cells would eventually give rise to the lymphocytes in blood. Lymphocytes are normally of two types – B cells and T cells. The majority of cases of ALL are of B-cell origin, but it can also arise from T-cell precursors. It can be diagnosed and differentiated from other forms of leukemia and lymphomas by the immunophenotype of the cells, cytochemistry and cytogenetic markers.

Causes and risk factors

Genetic and environmental causes have been cited. Environmental causes include exposure to radiation and chemicals like benzene.

Symptoms of ALL

The initial symptoms may appear slowly and the disease may progress rapidly and aggressively thereafter.

The symptoms worsen as the number of immature white blood cells in blood circulation rises to overcrowd the other types of cells.

Major symptoms include anemia or pale skin, fatigue and tiredness, breathlessness and repeated infection episodes and bruising and bleeding episodes that are frequent and unusual.

Epidemiology

Acute lymphoblastic leukaemia is the most common type of cancer to affect children. Approximately 1 in every 2,000 children will develop this cancer.

Standardised incidence rate is 1 per 100,000 general population per annum in England, Scotland and Wales.

ALL represents 12% of all leukaemia and 80% of all cancers in children. Around 85% of cases of ALL are seen in children aged under 15. Most cases are diagnosed between two and five.

Treatment and prognosis or outlook

ALL is usually treated with a combination of chemotherapy and radiotherapy. Bone marrow transplant is also used in some cases.

The outlook for children with ALL is usually good. Almost all children will achieve a remission and 85% will be completely cured. When diagnosed in adulthood chances cure is however lower (40%).