Acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) are different cancers of the blood. ALL and AML develop from two different cell types, respectively known as lymphoid cells and myeloid cells. Each different type of leukemia is likely to affect different types of people based on factors such as age and other conditions. Each may cause different symptoms, have different prognoses, and be treated with different therapies.
There are many different types of blood cells, all made by stem cells in the bone marrow tissue found inside certain bones. Different blood cells go on to have different jobs in the body. Blood cells are generally categorized into two main categories: lymphoid cells and myeloid cells.
Lymphoid cells are white blood cells that play a role in the immune system and help fight infections. Lymphocytes (B cells and T cells) and natural killer cells are all types of lymphoid cells.
Granulocytes are types of white blood cells, also called myeloid cells. There are a few types of granulocytes: neutrophils, eosinophils, and basophils. Other blood cells include red blood cells, which deliver oxygen to all of the body’s tissues, and platelets, which help clot the blood.
First, leukemia can be either acute or chronic: Acute leukemia cells are underdeveloped, don’t work properly, and grow quickly. Chronic leukemia cells are more mature, can carry out some of their normal jobs within the body, and grow slowly. In some cases, chronic myeloid leukemia (CML) is even curable.
Second, leukemia is classified into lymphoid or myeloid groups. Lymphoblastic or lymphocytic leukemias develop from lymphoid cells. Myeloid or myelogenous leukemias form from myeloid cells.
Putting the two categories together, there are four main types of leukemia:
AML is more common than ALL. In 2020, nearly 20,000 people were diagnosed with AML for the first time. On the other hand, a little over 6,000 people were diagnosed with ALL. These two types of cancers are both slightly more likely to affect men than women and occur more often in white people.
One major difference between these leukemias is that ALL is much more likely to affect children. Children make up about 60 percent of ALL cases. A child’s risk of developing ALL is highest under the age of 5. AML, however, usually affects older adults. The average age at diagnosis for a person with AML is 68 years old.
Some characteristics can increase a person’s chances of developing ALL or AML. Both leukemias share some of the same risk factors, including exposure to radiation or chemicals. ALL and AML are also both more likely to develop in people with certain genetic disorders, including:
Viral infections are also a risk factor for ALL, but not for AML. People who have previously been infected with HTLV-1 or the Epstein-Barr virus (EBV) have a slightly higher chance of developing ALL.
Other risk factors for developing AML include:
Both ALL and AML cause many of the same symptoms. Each of these types of leukemia can lead to general symptoms such as:
ALL and AML also lead to low levels of healthy blood cells, which can lead to additional conditions, including:
When ALL affects the T cells, it frequently leads to problems with the thymus (an organ in the chest, behind the breastbone). People with T-cell ALL may cough or have breathing difficulties. Thymus problems aren’t usually seen in B-cell ALL or in AML.
Leukemia treatment is often given in phases, each of which has a distinct purpose.
ALL treatment phases include:
AML is also typically treated with induction and consolidation therapy. Doctors have not traditionally used maintenance therapy when treating myeloid leukemias. This approach may change as new, more effective treatment options become available.
Induction therapy for both ALL and AML often begins with chemotherapy drugs. Chemotherapy may include one or a combination of medications. Sometimes, a targeted therapy is also added to the treatment plan, depending on which gene changes a person has.
Targeted therapy can attack specific genes or proteins that are found in cancer cells. For example, about 1 out of 4 adults with ALL has a change called the Philadelphia chromosome, in which two chromosomes (pieces of DNA) are abnormally attached. Leukemia cells that have this change can be killed with targeted therapy drugs like Gleevec (imatinib).
Likewise, people with AML caused by certain gene mutations may be able to use different targeted therapies.
If ALL or AML has spread to the brain or spinal cord, radiation therapy may be used to kill those cancer cells.
Both ALL and AML can be treated with a stem cell transplant. During this procedure, both the normal and leukemic cells in the bone marrow are destroyed with chemotherapy or radiation. Next, the recipient receives an infusion of healthy stem cells that make new, normal blood cells. ALL and AML are usually treated with allogeneic stem cell transplantation, in which the new stem cells come from a matched donor.
People with ALL often have a better prognosis (outlook) than people with AML do. About 69 percent of people with ALL live at least five years after diagnosis, whereas about 29 percent of people with AML live at least five years after diagnosis.
Some characteristics are linked to a better prognosis for people with ALL. Age makes a big difference in a person’s survival rate. Among adults over the age of 65, about 15 percent will live for at least five years. However, among children under the age of 15, more than 90 percent will live for at least five years.
A person’s ALL subtype also plays a large role. People with ALL that affects immature B cells tend to have a better outlook than people with ALL that developed from mature B cells.
Other prognostic factors that can lead to a good outcome include:
Age also plays a significant role in a person’s AML outlook. Although AML is not very common in younger people, children and younger adults have a better prognosis than older adults.
AML shares some of the same prognostic factors as ALL, but it has also been linked to other factors. Factors that may lead to a better outlook for people with AML include:
If a person with AML previously had another blood disorder — such as an MPN or MDS — they are likely to have a worse prognosis. Additionally, AML that developed following treatment for a different cancer usually leads to a worse outlook.
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