Leukemia

Leukemia is primarily a disorder of the body’s blood-forming tissues in which the normal elements are replaced with abnormal white blood cells. It involves the bone marrow and the lymphatic system. It accounts for one third of all childhood cancers. It is seen more prevalently in caucasian children than in any other race and it occurs more in males than in females.

Classification

Leukemia is classified as acute or chronic, lymphocytic or myelogenous and its classification is based on the type of cells involved and on the speed of progression.

With acute leukemia, you have a rapidly progressing disease involving abnormal, immature blood cells known as blast. These blood cells multiply so rapidly and are so immature, and consequently the disease worsens because the cells cannot carry out their normal work.   With chronic leukemia, the blood cells are more mature. The cells replicate and tend to accumulate more slowly and can even function normally for a short time. With chronic leukemia, the symptoms may not present themselves initially and in fact, may not manifest themselves for several years.

Lymphocytic Leukemia is a type of leukemia that involves the lymphoid cells (T-cells, B-cells, and pre-B cells) known as lymphocytes. These cells form lymphatic tissue which is part of your immune system.

Myelogenous Leukemia is a type of leukemia that involves the cells which arise from the blood forming tissue of the bone marrow. Myeloid cells help form your red blood cells, white blood cells and platelet-producing cells.

Etiology or Causes

Your white blood cells are the components in the blood that fight infection. Typically, they will grow and divide in an orderly way, to fit the needs of your body.  Lymphoid cells will grow and develop into lymphocytes and myeloid cells will grow and develop into red blood cells, granulocytes, monocytes and platelets. Lymphoid cell, granulocytes and monocytes are a type of white blood cell. However, with leukemia, the bone marrow produces abnormal white blood cells, which do not function in the proper manner. With the displacement of normal bone marrow cells with the higher number of immature white blood cells, the blood becomes deficient in the number of blood platelets which is an important component in the blood clotting process. Consequently, this will lead to easier bruising and bleeding.  With the immature white blood cells, you have dysfunction and the immune system becomes incompetent in its ability to fight off infection.  And finally, with the red blood cell deficiency, you can expect to see some fatigue, dyspnea (difficulty breathing) and pallor that you will typically see when a person is anemic.

Leukemia can develop at any time during the stages of normal blood cell development. The exact cause of leukemia remains unknown, however, genetics factors and chromosomal abnormalities may play a part in its development. One school of thought is that leukemia occurs when blood cells acquire a mutation in their DNA. Other changes within the cells, which are not completely understood, may contribute to the development of leukemia.

There are certain risk factors associated with this disease.

Those factors are:

  • Age 2-5 years old
  • Male gender
  • X-ray exposure in utero
  • Previous radiation-treated cancer
  • Ataxia telangiectasia, Down’s Syndrome and Shwachman Syndrome
  • Signs and Symptoms

Some of the more common signs and symptoms you will see includes fever, frequent infections, fatigue, listlessness, pallor, bone pain, abdominal pain, nausea and vomiting, bruising, tiny red spots on the skin (petechiae), recurrent nose bleeds, weight loss, swollen lymph nodes, possibly an enlarged spleen, and night sweats.

Diagnostic Test

Complete Blood Count:  You can expect to see an elevated, normal or decreased white blood cell count. Other findings will include low hemoglobin and hematocrit levels, a decreased platelet count and a decreased red blood cell count.

Bone Marrow Aspiration: The bone marrow aspirate is examined for the percentage of lymphoblast (> 25%), and also to examine for immuno-phenotyping.  Phenotyping is the process of classifying the type of cells involved, as well as, determining the level of mature cancer cells.  Cytogenetic analysis is the process used to determine abnormalities in chromosome structure and number.  Both cytogenetic analysis and immunophenotyping are used to determine the type of Leukemia, which is necessary to formulate a treatment plan.

Lumbar Puncture:  This procedure involves inserting a needle in the lower spinal column to obtain cerebrospinal fluid from the subarachnoid space. The fluid is examined to determine if leukemic cells have infiltrated the central nervous system.

Peripheral Blood Smear: The blood smear is examined for the presence of blast.

Comprehensive Metabolic Panel:  More specifically, doctors are looking at the liver function test components, as well as, the blood urea nitrogen and creatinine levels (both components used to assess kidney function). If the test results are abnormal, this may prohibit the use of certain chemotherapeutic agents. 

Treatment and Prevention

Treatment of leukemia can involve chemotherapy, radiation therapy, targeted therapy and possibly, bone marrow transplantation. Targeted therapy involves the use of an oral medication called “tyrosine kinase inhibitors or TKI’s. Tyrosine kinase is an enzyme that functions as an on/off switch for many cellular functions. The mechanism of action involves targeting tyrosine kinase and blocking its action. This slows or stops the growth of cancer cells.

Bone Marrow Transplantation

A Bone marrow transplant is a multi-step process. The first step involves finding a person, a donor (often a sibling), who will agree to contribute their bone marrow stem cells to the diseased person. The donor will then be tested to determine if their stem cells will be a match to the recipients.  If the donor and the recipient share the same Human Leukocyte Antigens (abbreviated as HLA), they are said to be a “match.”  This means that their tissues are immunologically compatible with each other. Next, the recipient’s bone marrow is depleted through radiation treatments and chemotherapy. Then, the donor’s stem cells are filtered from their blood and later injected intravenously into the recipient’s bloodstream.  These healthy stem cells will migrate into the bone marrow cavities where they will begin producing new blood cells. This process involves a lengthy hospital stay and typically, the patient is placed in isolation. There are risks involved with this procedure.  The recipient may reject the transplanted stem cells which can lead to life-threatening complications.  The treatment also may involve the use of drugs that will suppress the immune system. These drugs known as immune-suppressants, will aid in preventing the rejection of the donated stem cells.

Treatment of the child with leukemia also focuses on managing the symptoms and complications associated with this disease.  Antibiotics, pain medications and anti-emetics are used to fight infections, relieve the pain and control the nausea and vomiting.  Many children will require transfusions of blood products to treat the anemia and low platelet counts.  The blood products should be leukodepleted, irradiated, and cytomegalovirus (CMV)negative.  This is required to decreases the amount of antibodies in the blood (with blood transfusions, you are introducing the donor blood antibodies). Consequently, if a stem cell transplant becomes necessary, you diminish the chance of the child developing Graft Verse Host Disease, complication of the transplantation treatment.

Prognosis

The success of treatment is dependent on several factors; the type of leukemia and the age of the person. According to statistics, the average five-year survival rate is 57% in our country. For children, less than 15 years old, the five-year survival rate can be as high as 85%, contingent on the type of leukemia. In most cases of acute leukemia, if the child is cancer free for 5 years, the disease is unlikely to return.