Subtype and Classification of Acute Lymphocytic Leukemia

Executive Summary

Acute lymphocytic Leukemia, specific chromosomal or genetic changes in the cancer cells help plan treatment and predict prognosis. The subtypes of acute lymphoblastic leukemia include precursor B-cell ALL, precursor T-cell ALL, Burkitt-type ALL, Philadelphia chromosome-positive (BCR-ABL fusion) ALL. Unlike other types of cancer, there is no staging system for acute lymphoblastic leukemia. Instead, there are general classifications that are used to describe ALL that include newly diagnosed and untreated, in remission, refractory and recurrent or relapsed acute lymphoblastic leukemia.

Subtype and Classification of Acute lymphocytic Leukemia

Doctors divide ALL into subtypes and classify the disease based on the specifically affected lymphocytes. For instance, flow cytometry distinguishes ALL involving B cells or T cells. And so, specific chromosomal or genetic changes in the cancer cells help plan treatment and predict prognosis.

Subtypes include ^​1​:

• Precursor B-cell ALL
• Precursor T-cell ALL
• Burkitt-type ALL
• Philadelphia chromosome-positive (BCR-ABL fusion) Acute lymphocytic Leukemia (see below)

Types of Leukemia

Some patients have a type of leukemia called biphenotypic acute leukemia, mixed phenotype acute leukemia, or ambiguous lineage acute leukemia. This means that the disease has ALL or acute myeloid leukemia (AML) characteristics. Often, the same treatments used for ALL are also used for this type of leukemia.

As described in the diagnosis, about 20% to 30% of adults with ALL have a mutation or genetic change called the Philadelphia chromosome (Ph). This causes two genes, BCR and ABL, to become one fusion gene called BCR-ABL.

The Philadelphia chromosome is generally seen only in the cancerous blood-forming cells, not in other body organs, and is not inherited. Therefore, there are no worries about an increased ALL chance for other family members.

The BCR-ABL gene causes specific white blood cells known as B lymphoblasts to grow uncontrollably. Moreover, understanding whether a person has the BCR-ABL gene helps doctors predict a patient’s prognosis and suggest treatment. So, it is essential to test for it.

Around 20% to 25% of patients with precursor B-cell ALL have a type of ALL known as Ph-like ALL. The genetic modifications found in the leukemia cells of Ph-like ALL act like those associated with the Philadelphia chromosome. But, there are no signs of the Philadelphia chromosome in the leukemia cells. Instead, the leukemia cells have other mutations that act similarly. This means that the same treatments used for leukaemia with the Philadelphia chromosome may also work for Ph-like Acute lymphocytic Leukemia.

ALL Classification and Status of the disease

In other cancer types where a solid tumor forms, doctors agree on stages that describe how big the tumor is and where it has spread. There is no staging system for ALL because it usually does not form a solid tumor. And it is generally found throughout the body when diagnosed. Instead, there are general classifications that are used to describe ALL ^​2​–

Newly diagnosed and untreated

The bone marrow has abnormal lymphoblasts. However, the person may or may not show any symptoms. A patient mostly has decreased numbers of healthy red blood cells, white blood cells, and platelets. Some patients can have an overall increased number of white blood cells, but most may be abnormal lymphoblasts.

In remission

A patient has received treatment for ALL, and the bone marrow contains less than 5% blasts, and the patient shows no symptoms. The numbers of healthy red blood cells, white blood cells, and platelets are normal. New monitoring methods, such as minimal residual disease (cancer cells not destroyed by treatment), can better find tiny numbers of remaining blasts. Minimal residual disease methods are now being used more often to find out remission.

Refractory

Refractory leukemia means that the disease has not responded to treatment.

Recurrent or relapsed ALL

Recurrent leukemia has come back after remission. If leukemia does come back, there will be another round of tests to determine the extent of the recurrence. These tests and scans are usually similar to those done at the original diagnosis.

References