It is a cancer characterized by a large increase in the number of white blood cells (leukocytes) in the circulation or bone marrow.
Leukemia is found in the blood and bone marrow and is caused by the rapid production of abnormal white blood cells.
These abnormal white blood cells are unable to fight infection and impair the bone marrow’s ability to produce red blood cells and platelets.
Several different leukemias are classified according to the course of the disease and the predominant type of white blood cell involved.
Some types of leukemia have been linked to radiation exposure, as seen in the Japanese population exposed to the first atomic bomb in Hiroshima, other evidence suggests inherited susceptibility.
Types of Leukemia
Blood cells are made in the bone marrow, which is the spongy tissue inside the bones.
Blood-forming stem cells divide to produce more immature cells that develop into mature blood cells over time, both myeloid and lymphoid .
The myeloid stem cell can develop into one of three types of mature cells:
- In red blood cells responsible for transporting oxygen to all tissues of the body.
- In platelets responsible for forming blood clots to stop bleeding.
- In granulocytes or white blood cells, responsible for fighting infections and diseases.
The lymphoid stem cell can develop into lymphoblasts and later into one of three types of lymphocytes:
- In B lymphocytes responsible for producing antibodies to fight infections.
- In T lymphocytes responsible for helping B lymphocytes to produce antibodies to fight infections.
- In natural killer cells responsible for attacking cancer cells and viruses.
Leukemia affects white blood cells and can be classified by the type of white blood cell affected (myeloid or lymphatic) and by the way the disease progresses (acute or chronic).
Leukemia can occur acutely or chronically. Chronic leukemia progresses more slowly than acute leukemia, and requires immediate treatment.
Leukemia is also classified as lymphocytic or myelogenous.
Lymphocytic leukemia refers to abnormal cell growth in marrow cells that develop into lymphocytes, a type of white blood cell that plays a role in the immune system.
In myelogenous leukemia, abnormal cell growth occurs in cells in the marrow that mature into red blood cells, white blood cells, and platelets.
There are four broad classifications of leukemia:
- Acute lymphocytic leukemia.
- Acute myelogenous leukemia.
- Chronic lymphocytic leukemia.
- Chronic myelogenous leukemia.
Leukemia occurs in both adults and children.
Acute lymphocytic leukemia is the most common form of childhood leukemia, and acute myelogenous leukemia is the second most common.
Decades of research have led to vastly improved outcomes for children diagnosed with acute lymphocytic leukemia.
The two most common adult leukemias are acute myelogenous leukemia and chronic lymphocytic leukemia.
Acute leukemias affect immature cells, the disease develops rapidly.
Immature leukemia cells continue to divide in the bone marrow, leading to rapid death if left untreated.
In chronic leukemia, cells develop and are transported to tissues, but the cells do not function normally.
Myelogenous leukemia affects granulocytes and monocytes, white blood cells that destroy bacteria and some parasites.
With the use of proper treatment, most patients with acute lymphocytes now achieve complete remission, with no evidence of malignant cells in the blood.
With continued therapy, more than half remain disease free for five years or more. These patients are supposed to be cured.
Treatment results for other leukemias have not been as positive.
In acute myelogenous leukemia, which is more common in adults, patients may experience a complete remission, but recurrence is common.
Chronic leukemias also occur more frequently in adults. These are characterized by a more gradual onset and a longer course.
Chronic myelogenous leukemia, which has a peak incidence among adults in their 40s, can lie dormant for long periods before symptoms such as weight loss, low fever, and weakness appear.
If left untreated, chronic myelogenous leukemia can lead to a fatal phase known as a blast crisis, which occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells or blast cells.
This phase of Chronic Myelogenous Leukemia can last four to six months and is characterized by fever, weakness, and an enlarged spleen.
Chronic lymphocytic leukemia occurs mainly in the elderly and can be inactive for months or years.
Leukemia itself is rarely the cause of death, but it makes the patient vulnerable to infection or bleeding.
In most cases of leukemia there is no obvious cause. However, it is important to understand that:
- Leukemia is not a condition that can be spread from someone else.
- Leukemia is not passed from parent to child, it is not inherited.
Among the main risk factors are:
- Age : Most forms of leukemia are more common in older people. The main exception to this is anything where the peak incidence is in children.
- Gender: Leukemias are generally more common in men.
- Genetics: Although leukemia is not an inherited disease, there is a slightly higher chance that close relatives of patients will develop some forms of leukemia. The risk is still very small, and there is no reason for anxiety or screening.
- Exposure to chemicals : Exposure to some chemicals and high levels of radiation can increase your chances of developing leukemia. These factors represent only a very small proportion of all cases.
Some forms of leukemia are seen more often in people who have other bone marrow disorders.
The most common disorders that behave in this way are myelodysplastic syndrome and myeloproliferative neoplasms.
Symptoms of Leukemia
The signs and symptoms of leukemia and blood cancers are generally notoriously vague and nonspecific.
There are no specific signs or symptoms of any type of leukemia that allow the doctor to make a diagnosis without laboratory tests.
In all types of leukemia, symptoms are more commonly caused by a lack of normal blood cells than by the presence of abnormal white blood cells.
As the bone marrow fills with leukemia cells, it cannot make the large number of normal blood cells that the body needs. What causes:
- Red blood cells transporting oxygen to all tissues of the body.
- Weakness, tiredness, shortness of breath, lightheadedness, palpitations.
- Infections due to a lack of normal white blood cells.
- Infections are more frequent, more severe, and last longer.
- Fever, malaise (general ill feeling), and sweating.
- Purpura (small bruises on the skin), heavy periods, nosebleeds, bleeding gums.
- Bleeding and bruising due to lack of platelets.
There are some symptoms that are only seen in certain patients or forms of leukemia.
For example, young children with acute lymphocytic leukemia may complain of bone or joint pain, and in some types of acute myelogenous leukemia, the leukemia cells may swell the gums.
In lymphoid malignancies, the lymph nodes may be swollen.
In some forms of leukemia, the liver may be enlarged (hepatomegaly) or the spleen, an organ of the immune system just below the ribs on the left side, may be enlarged ( splenomegaly ).
The diagnostic process can seem long and frustrating.
It is important for your doctor to rule out other causes of a health problem before making a diagnosis of leukemia.
When symptoms are severe, the diagnosis of acute leukemia can occur quickly, and treatments must be started quickly.
The following tests are commonly used to rule out or diagnose leukemia.
Many of the same tests that are used to diagnose cancer are used to determine the stage, which is the extent to which the cancer has progressed.
Your doctor may also order other tests to monitor your general health and help plan your treatment.
Medical history and physical examination
The medical history is a record of symptoms, risk factors, and disease history and events.
Among the symptoms that suggest leukemia are:
- Exposure to high doses of radiation.
- Genetic syndromes such as Down syndrome, Fanconi anemia, ataxia-telangiectasia or Bloom syndrome.
- Exposure to benzene.
- Previous chemotherapy or radiation therapy.
- Blood disorders
- Viral infections
- Family history of leukemia.
The physical exam allows the doctor:
- Check vital signs for fever, shortness of breath, and a fast heartbeat.
- Check the skin for bruising and paleness.
- Feel areas in the neck, armpits, and groin for any lymph nodes that are swollen or enlarged.
- Check the mouth for infection, bleeding, or inflammation of the gums.
- Palpate the abdomen for enlarged organs.
- Examine the skeleton for pain.
Likewise, tests are carried out to make the diagnosis such as:
Blood count and other laboratory tests
A complete blood count measures the quantity and quality of white blood cells, red blood cells, and platelets.
Leukemia and other conditions can cause abnormal blood cell counts.
Immature blood cells (called leukemia cells or blasts) are not normally seen in the blood, so doctors will suspect leukemia if there are blasts or if the blood cells do not look normal.
Blood chemistry tests are used to measure certain chemicals in the blood.
They show liver or kidney function caused by the spread of leukemia cells.
Levels of the following chemicals may be higher than normal with leukemia:
- Blood urea nitrogen.
- Lactate dehydrogenase.
- Alanina aminotransferasa.
- Aspartate aminotransferase.
- Uric acid.
Tests that measure blood clotting factors reveal if there are abnormal levels, these are measured using the following tests:
- Fibrinogen levels.
- Prothrombin time.
- The partial thromboplastin time.
- The international normalized index.
Immunophenotyping is the study of the proteins expressed by cells and thus determine the type or subtype of leukemia.
Immunophenotyping uses a highly specific antigen-antibody reaction to identify proteins in tissues or cells.
It uses monoclonal antibodies labeled with a fluorescent tag or specific enzyme tag that binds only to specific antigens (proteins).
The fluorescent or enzymatic label allows you to see the leukemia cells (also called blasts).
Immunohistochemistry and flow cytometry are the 2 most common methods used in immunophenotyping leukemia.
Immunohistochemistry uses a microscope to view immunoperoxidase labels. It also allows doctors to see cells and their surroundings.
Flow cytometry is a technique used to classify cells using fluorescent labels on their surface.
The cells are exposed to a laser, which causes them to emit light.
Flow cytometry allows clinicians to view many antibodies at the same time and quickly collect data from thousands of cells in a single sample.
Flow cytometry helps define unique characteristics of leukemia cells or blasts.
These characteristics can help form a prognosis and measure response to treatment using minimal residual disease.
A small number of leukemia or minimal residual disease cells means that there are bursts in the bone marrow that cannot be found using standard laboratory tests (such as microscopy), but are found using more sensitive tests (such as flow cytometry or polymerase chain reaction).
Cytogenetics is the analysis of a cell’s chromosomes, including the number, size, shape, and way they are arranged.
Cytogenetic karyotype studies show chromosomal abnormalities, which help doctors confirm that someone has leukemia and discover the type or subtype of leukemia.
The results of cytogenetic studies also help doctors plan treatment and predict how well treatment will work.
Some important chromosomal abnormalities can be found by looking at cells under a microscope.
But most DNA changes need more detailed analysis with other molecular studies, including fluorescent in situ hybridization and polymerase chain reaction.
Fluorescent in situ hybridization is a molecular genetic test used to identify chromosomal abnormalities and other genetic changes in leukemic cells or blasts.
It uses special DNA probes labeled with fluorescent dyes.
Fluorescent in situ hybridization is used to differentiate leukemias that look the same, but have different genetic abnormalities and may need to be treated differently.
The polymerase chain reaction is a method used to make many copies of a particular genetic segment so that it can be tested in the laboratory.
The polymerase chain reaction is used to find DNA mutations, inversions, or deletions that are related to certain types of leukemia.
It is useful for diagnosing and determining the prognosis of a specific type of leukemia.
During a bone marrow aspiration and biopsy, cells are removed from the bone marrow so they can be analyzed in a laboratory.
The final report will confirm the leukemia cells present in the sample and the type of leukemia.
The lumbar puncture removes a small sample of the cerebrospinal fluid taken from the space around the spine to view it through a microscope.
A lumbar puncture is done to see if the cancer has spread to the spinal fluid.
A lymph node biopsy is a type of surgical biopsy, where the lymph node is completely removed, although sometimes the lymph node cannot be completely removed.
Pathologists then look at the lymph node under a microscope to check for cancer cells, identify the type of cancer, and find out how fast cancer cells are growing.
A chest X-ray uses small doses of radiation to make a picture of body structures on film. Used to search for:
- Enlarged lymph nodes in the center of the chest (called mediastinal lymph nodes).
- The thymus gland enlarged.
- The accumulation of fluid between the lungs and the walls of the chest (called a pleural effusion).
- A lung infection ( pneumonia ).
Computed tomography uses special x-ray equipment to obtain three-dimensional images of organs, tissues, bones, and blood vessels within the body.
A CT scan can be used to look at the spleen and liver to see if they are larger than normal.
It can also be used to check if lymph nodes around the heart, near the windpipe, or at the back of the abdomen are enlarged.
MRI is most often used when doctors think that leukemia has spread to the brain.
Ultrasound is used to look at internal organs, and to see if the kidneys, liver, or spleen have been affected by leukemia.
Staging is not widely used for leukemia, because it is already spread throughout the body when it is first diagnosed. However, there is a staging system for chronic lymphocytic leukemia.
In various types of leukemia, there are systems to classify leukemia as high-risk, standard, or low-risk.
Importantly, this refers to the possibility of a successful result after standard treatment.
If treatment is selected based on risk group, many patients with high-risk disease will do very well.
The risk group is only one of the factors that affects the outcome of treatment.
Some patients who have leukemia do not start treatment right away.
If patients are not being treated, they have regular check-ups. This is known as “watch and wait” or “active monitoring.”
This is mainly relevant for patients with chronic lymphocytic leukemia.
Almost all patients with chronic myelogenous leukemia or acute leukemia will begin treatment soon after diagnosis.
Some patients with chronic lymphocytic leukemia will never need treatment for their leukemia.
Acute leukemia is often curable with standard treatments.
Chronic leukemia is generally not curable, but it is treatable.
Although most chronic leukemia patients have a good initial response to treatment, sometimes the condition recurs, this is known as relapse, and can usually be re-treated using treatments similar to those used the first time. .
The main ways that leukemia is treated are:
- Chemotherapy: drugs to kill cells. Steroids are normally used along with chemotherapy for lymphoid leukemia.
- Radiation therapy: usually only for stem cell transplantation or a local disease, for example, in the spleen.
- Targeted therapy – Drugs that specifically recognize and kill leukemia cells.
- Biological therapy: Treatments that use the immune system to destroy leukemia cells. These often use antibodies to markers of leukemia; These are known as monoclonal antibodies.
- Stem cell transplant: Younger / fit patients may have a stem cell transplant (bone marrow transplant). This can be done using your own healthy stem cells or stem cells from a donor. This is most often done for acute leukemia if chemotherapy fails to cure the disease.
Chemotherapy is the use of drugs that kill cells. These kill cancer cells and prevent them from dividing.
Chemotherapy is usually given in blocks or “cycles” of treatment.
A course of treatment will consist of a series of chemotherapy doses followed by a break for healthy cells to recover.
Chemotherapy is usually given as a combination of drugs which, for lymphoid leukemia, will usually include steroids.
The steroids used to treat lymphoid leukemia are a laboratory-made version of chemicals produced naturally by the body.
The details of the treatment will vary depending on the characteristics of the leukemia and the general fitness of the patient.
Treatment side effects also vary between different types of treatment and different patients.
In some cases, leukemia or its treatments can cause serious problems.
These leukemia-related emergencies must be treated right away. The most commons are:
- Tumor lysis syndrome can occur when chemotherapy is given to treat acute leukemia, but cancer cells die quickly and the kidneys cannot remove substances they release from the blood quickly enough.
- Superior vena cava syndrome can occur when too many leukemia cells develop in the thymus, causing it to enlarge and block the windpipe. Superior vena cava syndrome can develop in patients with acute lymphocytic leukemia.
- Disseminated intravascular coagulation is a condition in which blood clots form in the bloodstream and bleeding also occurs. Disseminated intravascular coagulation can develop more often with acute promyelocytic leukemia, but also with other subtypes of acute myelogenous leukemia.