All about acute lymphoblastic leukemia (ALL)

Acute lymphoblastic leukemia is a bone marrow cancer that involves a specific type of white blood cells called lymphoblasts. This form of leukemia is a rare disease that affects children more frequently than adults, and more men than women¹.

Acute lymphoblastic leukemia (ALL) is a type of cancer that affects bone marrow, the part of the body where the different types of blood cells are produced. These are erythrocytes, red blood cells responsible for carrying oxygen; leukocytes, white blood cells that help the body fight infection; and thrombocytes, or platelets that play a role in blood coagulation.

ALL affects the stem cells that give rise to lymphoblasts, which are white blood cells at an early stage of development. Instead of maturing and traveling towards the blood, these abnormal ‘blasts’ (cells that have not reached maturity) grow and divide uncontrollably. They invade bone marrow, interfering with normal blood cell production. Blasts may also reach other organs, such as lymph nodes, the liver and the spleen.

This particularly aggressive form of leukemia is a diagnostic and therapeutic emergency. Over the last ten years, medical advances and the arrival of new treatments have led to a remarkable increase in cure rates, mainly in children, who tolerate chemotherapy better than adults.

What are the risk factors for ALL?

ALL, which is neither contagious nor hereditary, has no known cause or trigger factor. In the majority of cases, it occurs in subjects who were in good health before diagnosis. However, several risk factors have been identified:

• Exposure to ionizing radiation: accidental, therapeutic (radiation therapy), or occupational
• A history of chemotherapy, administered as treatment for a previous cancer
• The presence of certain genomic anomalies, including Down syndrome
• Pre-existing blood conditions

To begin treatment, the patient may undergo induction chemotherapy and be hospitalized for at least a month. This type of chemotherapy induces bone marrow aplasia, leading to a very substantial reduction in the number of blood cells. It aims to eliminate cancer cells, which will allow blood cells to regenerate normally.

Consolidation 

In addition, consolidation is sometimes suggested. This involves a bone marrow transplant of hematopoietic stem cells. Donations can come from a compatible donor (family, donor registry), but can also be obtained from placental/umbilical cord blood (PCB), also called cord blood.

Maintenance

Cancer cells can infiltrate the meninges, membranes surrounding the brain and spinal cord. This neuro-meningeal involvement is a major cause of relapses in the first year of treatment. To prevent these, outpatient maintenance treatments such as cranial radiotherapy (PCR)and/or intrathecal (IT) chemotherapy may be administered for two years.

In the event of relapse, more chemotherapy is prescribed, starting with reinduction therapy, followed by additional maintenance and consolidation phases. A hematopoietic stem cell transplant may also be considered, originating from healthy donors (allograft).

New therapeutic approaches

While the response rates observed after standard treatments are generally high, some patients will experience drug resistance or relapse. Research has shown that cancer cells can develop mechanisms for escaping the patient’s immune system, which enables them to slip under the radar and not be recognized as dangerous. These cancer cells can then multiply unchecked in the patient’s body.

New therapeutic approaches to treat these patients are being studied. Today, they are at varying stages of development. Some may target the immune system in order to restore its ability to destroy cancer cells. These targeted therapies are based primarily on the use of specific antibodies for certain tumor cell markers, and immunotherapies.