B Precursor Type Acute Leukaemia

B-cell acute lymphoblastic leukemia, B-ALL, precursor B-cell lymphoblastic leukemia, precursor B-cell ALL, pre-B-ALL

B precursor type acute leukaemia is the most common form of acute lymphoblastic leukaemia in both children and adults, accounting for about 75% of all cases. While it poses significant challenges, it has become one of the most treatable cancers in children, with survival rates above 90%.

Table of contents

• What is B precursor type acute leukaemia?
• How it affects the body
• Who gets this disease
• Causes and risk factors
• Signs and symptoms
• How it is diagnosed
• Outlook and survival

What is B precursor type acute leukaemia?

B precursor type acute leukaemia is a rare blood cancer that affects the development of B cells, which are white blood cells that help the body fight off infections^[1]. The disease is also commonly called B-cell acute lymphoblastic leukemia or B-ALL^[2].

The term “acute” describes how the disease behaves. It means the cancer develops suddenly and progresses quickly over days or weeks^[1]. This is different from chronic leukaemia, which usually develops very slowly over months or years^[1].

In this disease, the bone marrow (the soft inner part of bones where blood cells are made) produces too many abnormal, immature B cells called lymphoblasts or blast cells^[2]. These abnormal cells are not fully developed and cannot work normally. They grow and divide quickly^[1].

As these abnormal cells build up in the bone marrow, they stop healthy blood cells from developing. The abnormal cells then spill over into the blood, allowing them to spread to other areas of the body quickly^[2].

• Bone marrow
• Blood
• Lymph nodes
• Liver
• Spleen
• Brain and spinal cord
• Testicles (rarely)

How it affects the body

To understand how this disease affects you, it helps to know how your body normally makes blood cells. Your body produces blood cells in the bone marrow. All blood cells start as the same type of cell, called a stem cell^[1].

This stem cell develops into either lymphoid stem cells or myeloid stem cells. Lymphoid stem cells develop into white blood cells called lymphocytes, which include B lymphocytes and T lymphocytes^[1].

In B precursor type acute leukaemia, the bone marrow makes too many B lymphocytes that are not fully developed. These abnormal cells build up in the bone marrow and stop healthy blood cells from developing. They also spill out into the blood and can spread into other parts of the body^[1].

Organs such as the lymph nodes, liver, and spleen may swell as abnormal B cells build up in these tissues. The disease may also spread to the brain, spinal cord, and testicles, although spread to the testicles is rare^[2].

Who gets this disease

B precursor type acute leukaemia is the most common type of acute lymphoblastic leukaemia. Around 75 out of every 100 people with ALL (around 75%) have this type^[1].

The disease is most common in children, making it the most common type of childhood leukaemia. Around 75% of all B-ALL cases affect children younger than six years old^[2]. However, it can occur at any age and does affect adults as well^[1].

Around 75% of adults with acute lymphoblastic leukaemia have the B-ALL subtype^[2].

Causes and risk factors

Researchers think that changes (called mutations) in genes that regulate B cell development cause B precursor type acute leukaemia^[2]. These genetic changes prevent the cells from fully developing into mature B cells and can also lead them to start growing and dividing out of control. The exact cause of these genetic mutations is not known^[2].

The risk of developing this disease increases in children who have certain conditions or exposures. These include^[2]:

• A family history of leukaemia, especially in siblings
• Genetic conditions, such as Down syndrome
• Previous exposure to X-rays, radiation, or chemotherapy
• Suppressed immune systems, usually from treatments following organ transplantation

Signs and symptoms

People with B precursor type acute leukaemia usually need to start treatment quite quickly after being diagnosed because the disease develops rapidly^[1].

Signs and symptoms of the disease may include^[2]:

• Decreased appetite and unintentional weight loss
• Difficulty breathing
• Easy bruising or excessive bleeding, especially of the nose and gums
• Fatigue or feeling unusually tired
• Pain in joints, bones, and abdomen (belly pain may occur due to an enlarged liver or spleen)
• Recurrent fevers and frequent infections
• Swelling of lymph nodes

How it is diagnosed

To diagnose B precursor type acute leukaemia, your doctor performs a physical exam and asks about your medical history^[2].

Several tests may be used to confirm the diagnosis^[2]:

Blood tests count the number of platelets, white blood cells, and red blood cells in a sample of your blood. Doctors also use blood tests to check liver and kidney function and to detect signs of inflammation and infection^[2].

Bone marrow aspiration or biopsy is the most common and reliable method for diagnosing this disease. Your doctor uses a thin, hollow needle to remove small samples of bone marrow or bone tissue for analysis^[2].

Imaging tests help determine the severity of the cancer and locate affected lymph nodes and tumors. They also detect enlarged organs, such as the liver or spleen. Imaging may include chest X-rays, CT scans, MRI scans, PET scans, ultrasounds, or echocardiograms^[2].

Lumbar puncture (also called a spinal tap) may be performed to check if the disease has spread to the brain or spinal cord^[2].

Doctors work out the specific type by looking at the structure and features of the leukaemia cells. The most common subgroup of B-cell ALL is precursor B cell ALL^[1]. Knowing the exact type helps your doctor decide which treatment you need.

Outlook and survival

The outlook for B precursor type acute leukaemia varies greatly depending on age. Children with this disease have very high cure rates. Around 85% of children with B-ALL stay cancer free after five years^[2]. The five-year survival rate for B-ALL is above 90% in children^[2].

Thanks to tremendous advances in understanding the biology of this disease, identification of prognostic markers, and improvements in treatment, B precursor type acute leukaemia has become the most curable cancer in children, with a long-term survival rate close to 90%^[6].

The outlook is not as favorable for adults. The five-year survival rate for B-ALL is around 40% in adults over age 20^[2]. For those aged between 15 and 39, around 65 out of 100 people (65%) will survive their leukaemia for 5 years or more after diagnosis. For those aged 40 and older, around 25 out of 100 people (around 25%) will survive their leukaemia for 5 years or more after diagnosis^[22].

The prognosis remains challenging for adults and children with relapsed disease. Relapsed B-ALL continues to be the leading cause of cancer-related death in children and young adults^[6].

Treatments can work well for some people with this disease, but survival depends on many factors including age, early response to treatment, and specific genetic features of the cancer cells^[1].