Your pathology report for acute lymphoblastic leukemia (ALL)

by Jason Wasserman MD PhD FRCPC and Aleksandra Paliga MD FRCPC
August 18, 2025

Acute lymphoblastic leukemia (ALL) is a type of blood cancer that starts in the bone marrow, the spongy tissue inside bones where blood cells are made. In ALL, the bone marrow produces large numbers of immature white blood cells called lymphoblasts or leukemic blasts. These abnormal cells grow quickly and crowd out the normal blood cells, which prevents the bone marrow from making enough healthy red blood cells, white blood cells, and platelets.

Although ALL is most often diagnosed in children, it can also occur in adults. When the same type of cancer develops outside of the bone marrow and blood, it is called lymphoblastic lymphoma.

What are the types of acute lymphoblastic leukemia?

ALL is classified based on which type of white blood cell, called a lymphocyte, is affected.

There are two main types ALL:

B-cell acute lymphoblastic leukemia (B-ALL): This type starts from immature B lymphocytes, a kind of white blood cell that normally helps fight infection by making antibodies. B-ALL is the most common type of ALL, especially in children. Learn more about your pathology report for B-ALL.

T-cell acute lymphoblastic leukemia (T-ALL): This type starts from immature T lymphocytes, white blood cells that normally help control the immune response and fight viruses. T-ALL is less common than B-ALL and tends to occur more often in older children, teenagers, and young adults. Learn more about your pathology report for T-ALL.

Who gets acute lymphoblastic leukemia?

ALL can occur at any age, but it is most commonly diagnosed in children between 2 and 5 years old. There is another, smaller peak in adults over the age of 50. Overall, the disease is slightly more common in males than in females. Certain groups, including people of Hispanic and white backgrounds, have a higher risk of developing ALL.

What are the symptoms of acute lymphoblastic leukemia?

The symptoms of ALL are mostly due to the bone marrow being unable to produce enough normal blood cells. This happens because the abnormal lymphoblasts take up most of the space in the bone marrow.

Common symptoms of ALL include:

  • Fatigue and weakness caused by low red blood cells (anemia).

  • Frequent fevers and infections caused by low levels of infection-fighting white blood cells (neutropenia).

  • Easy bruising or bleeding caused by low platelet counts (thrombocytopenia).

  • Bone and joint pain due to the buildup of abnormal cells inside the bones.

  • Swollen lymph nodes, liver, or spleen caused by the spread of leukemia cells.

  • Unexplained weight loss or loss of appetite.

Because these symptoms can also be caused by other conditions, blood tests and bone marrow examination are needed to make the diagnosis.

What causes acute lymphoblastic leukemia?

The exact cause of ALL is not fully understood, but several factors can increase the risk of developing this disease:

  • Genetic conditions: Certain inherited conditions, such as Down syndrome, are linked with a higher risk of ALL.

  • Environmental exposures: Previous treatment with chemotherapy or radiation therapy, and possibly exposure to certain chemicals, can increase the risk.

  • Random genetic mutations: In many cases, ALL happens when random changes occur in the DNA of bone marrow cells. These changes are not inherited but happen by chance.

How is this diagnosis made?

The diagnosis of ALL can only be made after examining blood and bone marrow samples. A complete blood count (CBC) is usually the first test performed. This test measures the number of red blood cells, white blood cells, and platelets in the blood. In people with ALL, the white blood cell count may be very high or very low, and immature cells called lymphoblasts may be seen circulating in the blood.

Because blasts in the blood can sometimes look similar to normal immature cells, a bone marrow biopsy is usually needed to confirm the diagnosis. In this procedure, a small amount of bone marrow is removed, most often from the hip bone, and examined under a microscope by a pathologist. In ALL, the bone marrow shows an abnormally high number of blasts that crowd out the normal developing blood cells.

Additional tests are often performed to better classify the leukemia. Special stains and immunohistochemistry (tests that use antibodies to look for specific proteins on the blasts) can determine whether the blasts are of B-cell or T-cell origin. Flow cytometry, a laboratory test that analyzes cells as they pass through a laser beam, provides detailed information about the markers on the surface of the blasts. Molecular tests may also be performed to identify specific gene mutations or chromosomal changes, which are important for guiding treatment and predicting prognosis.

Questions to ask your doctor

If you have been diagnosed with acute lymphoblastic leukemia, you may find it helpful to ask your doctor the following questions:

  • What type of acute lymphoblastic leukemia do I have (B-cell or T-cell)?

  • What tests were done to confirm the diagnosis, and what did they show?

  • Has the leukemia spread outside of my bone marrow or blood?

  • What treatments are recommended for me, and what are their possible side effects?

  • How will my response to treatment be monitored over time?

  • What factors affect my prognosis (outlook) in my case?

  • Are there any clinical trials or newer treatments that I should consider?

A+ A A-