Leukemia is a term that encompasses several different types of blood cancers. The different types of leukemia are varied in their presentation, age of onset, risk factors and outlook.
Types of leukemia
There are four main types of leukemia:-
- Acute lymphoblastic (lymphocytic) leukemia (ALL)
- Acute myeloid (myelogenous) leukemia (AML)
- Chronic lymphocytic leukemia (CLL)
- Chronic myeloid (myelogenous) leukemia (CML).
Pathology
The basic tenet that is common in all leukemias includes the fact that they all begin in cells in the bone marrow. The bone marrow normally is responsible for generating the blood cells – red blood cells and white blood cells. One of the functions thus is to produce myeloid cells or white blood cells.
The growth and maturity of the bone marrow cells in these functions is tightly regulated by the cellular DNA. When the cell undergoes a change due to damage and changes in the DNA it becomes a leukemia cell and begins to proliferate uncontrollably.
Myeloid or myelogenous leukemia can begin in the cells that produce myeloid cells - red cells, white cells and platelets. Another type of cells affected is those that produce lymphocytes. Lymphocytic or lymphoblastic leukemia can arise in these cells.
Cause of leukemia
The exact cause of leukemias is unknown. As the bone marrow cells become leukemia they crowd the marrow and suppress other healthy cells. The rate of progression and replacement of normal bone marrow cells is different with each type of leukemia.
Who does leukemia affect?
Leukemia affects a large population of individuals worldwide. Around 274,930 people in the United States are living with, or in remission from, leukemia. In the UK, around 7,600 people are diagnosed each year with leukaemia.
People can get leukemia at any age. Those over 60 are more at risk. The most common types in adults are AML and CLL.
ALL is the most common form of leukemia in children. For AML, specific risk factors have been found. This includes earlier exposure to chemotherapy, Down’s syndrome and other genetic disorders, exposure to benzene and other chemicals, exposure to radiation therapy etc.
Signs and symptoms of leukemia
There are several signs and symptoms of leukemia that are common to all types. Specific blood tests and bone marrow tests are needed to make a diagnosis. In acute leukemias common symptoms include:
- lack of energy
- fatigue
- anemia
- prolonged fever
- night sweats
- unexplained bruises
- prolonged bleeding tendencies
- propensity to catch infections etc.
People with CLL or CML may not have any symptoms. CLL may manifest with enlarged lymph nodes in the neck, armpit or groin.
Diagnosis, treatment and outcome
Treatment, diagnosis and approach to each type of leukemia is different. ALL and AML (acute leukemias) are each composed of young cells, known as lymphoblasts or myeloblasts. Routine blood tests with complete blood counts help in diagnosis.
Bone marrow tests (aspiration and biopsy) are often done to confirm the diagnosis and to look for chromosome abnormalities. These tests identify the leukemia cell-type. Each main type of leukemia also has different subtypes.
Acute leukemias progress rapidly without treatment. CLL and CML, on the other hand have few or no blast cells. CLL and CML often progress slowly compared to acute leukemias without treatment. Today, more and more leukemia patients are in complete remission at least five years after treatment. The aim of therapy is to achieve complete remission.
Treatment for patients with acute leukemia may include chemotherapy, stem cell transplantation etc. Those with ALL and AML, start with treatment immediately after diagnosis using chemotherapy. The first part of treatment is called induction therapy. Treatment is given after remission. This is called the consolidation (intensification) therapy and maintenance therapy. This part of treatment may include chemotherapy with or without stem cell transplantation (sometimes called bone marrow transplantation).
Patients with CML need treatment soon after diagnosis. The drugs that can be used include imatinib mesylate (Gleevec®), dasatinib (Sprycel®) or nilotinib (Tasigna®). These are oral drugs that target the cancer specifically. Allogeneic stem cell transplantation is another treatment option for CML.
CLL usually progresses slowly without treatment and some CLL patients do not need treatment for long periods of time after diagnosis. Patients who need treatment may receive chemotherapy or monoclonal antibody therapy in combination. Allogeneic stem cell transplantation is a treatment option in some subgroups of patients.
Further Reading
Scientists identify drug-resistant bone marrow cells linked to poor outcomes in fast-growing leukemia