Leukemia is a malignant disease that affects bone marrow and lymphatic system and leads to formation of abnormal white blood cells that remain in the blood stream for longer period. The buildup of these cells prevents them from doing their functions and may interrupt other healthy cellular components of the blood.

Several types of leukemia are there. The classification is based on the diseased cells and the speed of progression. Most common four types of leukemia are: Acute myelogenous leukemia (AML), Acute lymphocytic leukemia (ALL), Chronic myelogenous leukemia (CML), Chronic lymphocytic leukemia (CLL).

Although the direct cause of leukemia is not determined, some factors participate in developing the disease, such as family history, smoking and past cases of cancer and cancer treatment. Even though avoiding as possible of these factors will decrease the risk of having leukemia.

Acute Leukemia may be noticed obviously by symptoms like tiredness, shortness of breath, paleness, poor wound healing and recurrent infections. These symptoms may delay with chronic forms, or they could not appear until the disease has discovered suddenly by a routine blood test.

Cancer treatment has developed greatly since the nearly 7 decades. Many therapies are available and effective, including chemotherapy, targeted therapy, radiation therapy, stem cell transplant and Immunotherapy. Patients relatively have high remission rates from leukemia. Nowadays, five-year Relative Survival Rates generally exceeds 50%.

Leukemia is a type of cancer that affects body's blood-forming tissues, including the bone marrow and the lymphatic system, that result in producing abnormal white blood cells that crowd out the healthy blood cells, making it hard for blood to do its work.

The type of leukemia depends on the type of blood cell that has become cancerous and how quickly the disease develops and gets worse. The main four types of leukemia are:

• Acute myelogenous leukemia (AML) affects myeloid cells and grows quickly. Leukemic blast cells collect in the bone marrow and blood. It can be a difficult disease to treat and it common in adults;
• Acute lymphocytic leukemia (ALL) affects lymphoid cells and grows quickly. Leukemic blast cells usually collect in the bone marrow and blood. The condition can Progress rapidly without treatment. ALL is the most common form of leukemia in children;
• Chronic myelogenous leukemia (CML) affects myeloid cells and usually grows slowly at first. Blood tests show an increase in the number of white blood cells. The abnormal blood cells work okay. There may be a small number of leukemic blast cells in the bone marrow;
• Chronic lymphocytic leukemia (CLL): considered the most common type of leukemia in adults, which affects lymphoid cells and usually grows slowly. Blood tests show an increase in the number of white blood cells. The abnormal cells work almost as well as the normal white blood cells.

Other types of leukemia are less common. They include: Hairy Cell Leukemia, Chronic Myelomonocytic Leukemia, Juvenile Myelomonocytic Leukemia, Large Granular Lymphocytic Leukemia, and Blastic Plasmacytoid Dendritic Cell Neoplasm.

Scientists don't know the exact causes of leukemia. It seems to develop from a combination of genetic and environmental factors. In general, leukemia is thought to occur when some blood cells acquire mutations in their DNA. There may be other changes in the cells that have yet to be fully understood could contribute to leukemia. Of those what lead the cells to grow and divide more rapidly and to continue living when normal cells would die.

For most types of leukemia, the risk factors and possible causes are not well-known. Specific risk factors are related to certain types of cancer. However, most people do not have these risk factors, and most who have do not get leukemia.

• Previous cancer treatment. People who've had certain types of chemotherapy and radiation therapy for other cancers have an increased risk of developing certain types of leukemia;
• Genetic disorders. Genetic abnormalities seem to play a role in the development of leukemia. Certain genetic disorders, such as Down syndrome, are associated with an increased risk of this disease;
• Exposure to certain chemicals. Benzene - which is found in gasoline and is used by the chemical industry - also is linked to an increased risk of acute myelogenous leukemia (AML);
• Smoking. The only proven lifestyle-related risk factor for AML is smoking. That’s may be related to as much as half of the personal exposure to benzene is from cigarette smoke;
• Family history. The risk of leukemia is more with first degree relatives of CLL patients, or having an identical twin who has or had AML or ALL;
• Gender: Men are more likely to develop CML, CLL and AML than women;
• Age: The risk of most leukemia typically increases with age, with the exception of ALL.

All blood cells come from blood stem cells that mostly exist in the bone marrow. They responsible for the production of red blood cells, platelets, and white blood cells. When blood cells become old or damaged, they die, and the blood stem cells produce new cells to replace it. A blood stem cell can produce both myeloid stem cells (can produce red blood cells, platelets and myeloblasts) and lymphoid stem cells (produce different types of white blood cells).

In case of leukemia, the bone marrow produces abnormal white blood cells that are called leukemia cells and leukemic blast cells. Leukemia cells divide to produce copies of themselves. The copies divide again and again, producing more and more leukemia cells. Unlike normal blood cells, leukemia cells don’t die when they become old or damaged. They can build up and crowd out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to the tissues, control bleeding, or fight infections.

Leukemia symptoms vary, depending on the type of the disease.

• Common acute leukemia signs and symptoms include:
  • Tiredness or lack of energy;
  • Shortness of breath during physical activity;
  • Paleness of skin;
  • Mild fever or night sweats;
  • Slow healing of cuts and excess bleeding;
  • Black-and-blue marks (bruises) for no clear reason;
  • Pinhead-size red spots under the skin;
  • Aches in bones or joints;
  • Low white cell counts, especially monocytes or neutrophils.
• Chronic leukemia: People with chronic types of leukemia may not have any symptoms. Some patients learn they have it after a blood test as part of a regular checkup. However, some of them may experience:
  • Enlarged lymph nodes in the neck, armpit or groin;
  • Feeling of tiredness or short of breath;
  • frequent infections if the condition is more severe;
  • Enlarged spleen (leading to Pain or fullness in the left upper abdomen);
  • Night sweats;
  • Unreasonable weight loss.

People with acute leukemia may develop sign and symptoms that suggest this disease. On the other hand, Doctors may find a sign for chronic leukemia in a routine blood test, before symptoms begin. To confirm the findings the doctor may order:

• Complete Blood Count (CBC) tests. A comprehensive blood cellular components examination that shows number, shape and size of deferent types of blood cells. This blood test may show high or low levels of white cells and show leukemia cells in the blood. Sometimes, platelet counts and red cell counts are low which may suggest leukemia after excluding other causes;
• Bone marrow test. Are often done to confirm the diagnosis and to look for chromosome abnormalities. In this procedure, the doctor takes a sample of bone marrow from the hipbone using a long, thin needle. The sample is sent to a laboratory to look for leukemia cells. Specialized tests of leukemia cells may reveal certain characteristics that are used to determine treatment options.

Additional tests, such as chromosome testing, may be undergone to confirm the diagnosis and to determine the type of leukemia and its extent in the body. Certain types of leukemia are classified into stages, indicating the severity of the disease. Leukemia’s stage helps the doctor determine a treatment plan. This test can be repeated after treatment begins to measure how well the treatment is working.

The aim of leukemia treatment is to bring about a complete remission. Treatment for the disease depends on many factors. The doctor determines leukemia treatment options based on the age and overall health, the type of leukemia, and whether it has spread to other parts of the body.

• Watchful waiting. Chronic leukemia without symptoms may not need treatment right away. When the disease worsens, treatment can often control the disease and its symptoms. The purpose is to avoid the side effects of treatment as long as possible. If the patient and the doctor agree that watchful waiting is a good idea, he will get exams and blood tests every 3 to 6 months. The doctor may suggest starting treatment if symptoms have developed. However, people with acute leukemia need to be treated right away;
• Chemotherapy. Chemotherapy is the major form of treatment for leukemia. This drug treatment uses chemicals to kill leukemia cells. Depending on the type of the disease, the patient may receive a single drug or a combination of drugs. These drugs may come in a pill form, or they may be injected directly into a vein. Patients with an acute leukemia need to start treatment soon after diagnosis. Cases of chronic leukemia may also benefit from this therapy;
• Targeted therapy. Targeted cancer therapies are drugs or other substances that fight cancer by interfering with specific molecules that are involved in the growth, progression, and spread of cancer. This therapy is more specific than chemotherapy with lesser side effects, as it acts on certain molecules that causes leukemia cells to grow. Also, it is often cytostatic (prevent expansion of tumor) rather than killing all rapidly dividing normal and cancerous cells in case of chemotherapy (cytotoxic);
• Radiation therapy. Using X-rays or other high-energy beams to damage leukemia cells and stop their growth. During radiation therapy, the patient lies on a table while a large machine moves around him, directing the radiation to precise points on the body. The patient may receive radiation in one specific area of the body where there is a collection of leukemia cells, or over the whole body as apart of other treatments as that used to prepare for a stem cell transplant; the next will be discussed;
• Stem cell transplant. It is a procedure to replace diseased bone marrow with healthy bone marrow. Before a stem cell transplant, the patient receives high doses of chemotherapy or radiation to destroy unwell bone marrow. Then receiving an infusion of blood-forming stem cells that help to rebuild bone marrow. The patient may receive stem cells from a donor, or in some cases from his own. A stem cell transplant is very similar to a bone marrow transplant;
• Immunotherapy: Also called biological therapy, this treatment utilizes the immune system to fight cancer. It generally results in fewer short-term side effects than chemotherapy does. It is based on the concept that immune cells or antibodies that can recognize and kill cancer cells can be produced in the laboratory and then given to patients to treat cancer. This therapy may be used alone or in combination with other types of cancer treatment.

• Infections: The immune system of People with leukemia is likely to be compromised either by disease process or during treatment as a side effect of chemotherapy. As a result, they are more vulnerable to develop an infection, which could be more serious than usual. Complications arising from infections are a leading cause of death among them;
• Bleeding: Having leukemia makes the person bleeds and bruises more easily and heavily due to the low levels of platelets in the blood. Affected with advanced forms of this cancer are more prone to have life-threatening internal bleeding;
• Anemia: myelogenous types of leukemia are under risk to have depletion in red blood cells (RBCs) as the precursor for its production (myeloid stem cells) is affected by the disease. Treating all types of leukemia with chemotherapy also affects negatively RBCs production and may lead to anemia;
• Second Cancers: Having any type of leukemia increases the risk of developing another form of cancer through patient’s life. This may be referred to sharing environmental or genetic and family factors, or may be linked to certain cancer treatments, such as radiation exposure and chemotherapy. The most frequent secondary cancer is skin cancer;
• Metastasis: One of the most serious risks of cancer is the ability spread in the body. Cancer cells can pervade the nearby tissue or lymph nodes and can reach distant parts and organs to cause complicated situation. The most common places where spreading of leukemia cells is found outside the bone marrow are spinal fluid, (CNS leukemia) liver, spleen, lymph nodes, and testicles;
• Treatment complications: Chemotherapy drugs can cause dozens of unwelcome side effects, such as fatigue, nausea, hair loss, infertility, anemia and infection. People who receive stem cells from a donor may get graft-versus-host disease, where the donated white blood cells react against normal tissues in the recipient and harm the liver, skin, or digestive tract. They are also under sever risk for infection and bleeding during this treatment.

There is no known way to prevent most types of leukemia. However, some types of this disease may be prevented by avoiding risk factors mentioned above. If the person had leukemia and got treatment, maintenance therapy may be used to prevent any remaining leukemia cells from growing. This may be done using lower doses of chemotherapy than those used during induction or consolidation. Here, the drug is given with pills and once-a-month intravenous (IV) treatment for up to 3 years.

The outcome for people with leukemia varies by the type of the disease, stage of cancer, age and health status of the patient. Modern treatments have led to a greater than fourfold increase since 1960 in 5-year survival rates for leukemia. According to an estimation of five-year Relative Survival Rates for leukemia Cancers among Individuals Aged 15 and Old in Select Countries from 1999-2006, the mean percent of lived persons was 50.1%.

The disease has the chance to reoccur after complete remission; so the patient need regular checkups after completes treatment. Someone with acute leukemia may need a checkup every month for the first year after treatment, and those with chronic leukemia may need a checkup every six months. Some cancer survivors may develop a new, unrelated cancer later. This is called "second cancer".

According to world cancer fund research international, leukemia occupies the 11th place in the most common types of cancers, with 352.00 cases worldwide in 2012, representing 2.5% of all cancers. More men are having leukemia than women do, with 201.000 and 151.000, respectively. The disease is more prevalent in developed countries than it is in less developed. Leukemia is the most common childhood cancers. However, it most often occurs in adults older than 55 years.