Acute and chronic leukemia. Pathomorphology of target organs: bone marrow, spleen, liver, lymph nodes
Leukemia is a group of cancers, originating in the bone marrow, that cause high numbers of (immature) white blood cells.
First, we need to remember, what are myeloid and lymphoid cells, and more specifically, what are myeloblasts and lymphoblasts?
Right, types of leukemia
- We can divide based on the lineage affected:
- Myeloid
- Lymphoid
- And based on onset
- Chronic
- Acute
First, let’s take an overall look at the four main types of leukemia.
Acute lymphoblastic leukemia
- Overproduction of immature white blood cells (lymphoblasts). This overproduction occurs in the bone marrow, and sees a reduction in lymphoblast quality
- Most common occurrence in childhood 2-5 years of age
- Symptoms include increased risk of bacterial infection, dyspnea, chest pain, tendency to bleeding and general anemic symptoms
- Thought to be a cancerous gene affecting the lymphoblast
- Can be further subcategories based on if it affects T- or B-lymphocytes more
- T-ALL goes on to cause thymic (mediastinal) mass, more common in teenagers
- Most common blood neoplasm in children
Chronic lymphocytic leukemia
- Most common type of leukemia affecting adults
- B-cells grow in uncontrolled manner and accumulate in bone marrow where they crowd out healthy blood cells
- Results in swollen lymph nodes, spleen and liver, eventually with anemia and infections. In a minority of patients it transforms into an aggressive lymphoma (Richter transformation)
Acute Myeloid leukemia
- Cancer of myeloid line with rapid growth of cells that build up in bone marrow and effect other normal cell production
- Rare, treated with bone marrow replacement therapy, more common in older adults
- One important subtype is acute promyelocytic leukemia (t(15;17)), these increase risk of DIC
- Can also categorise based on cell, monoblast AML or Megakaryoblast AML
- Symptoms include infections, anemia, and frequent bleeding
Chronic Myeloid leukemia
- Gradual proliferation of myeloid cells in bone marrow
- Linked with genetic abnormality known as Philadelphia chromosome (t9;22, BCR-ABL)
- Causes myeloid cells to divide beyond what they should normally, creating many granulocytes at all stages of maturation
- Causes hepato and splenomegaly
- Mainly affects adults aged 25-60
- Has a Chronic, Accelerated and Blast (crisis) phase
In acute leukemias, peripheral blood smears show a high prevalence of blast cells, these are larger than normoblast cells and lower in cytoplasm than their contemporaries. Myeloblast and Lymphoblast cells look identical under microscope, and chemical markers must be used to distinguish between the two.
- Lymphoblasts have TdT+ nuclear staining
- Myeloblasts have myeloperoxidase enzyme (cytoplasmic staining/observation of auer rod)