Blood Cancer

Every 3 minutes in the U.S., someone is diagnosed with a blood cancer. For many patients, a bone marrow transplant is the best chance for survival. While 30% of patients can find a matching donor in their families, 70%—nearly 14,000 each year—must rely on a benevolent stranger to step up and donate. Web Source  


Thousands of people with blood cancers like leukemia, lymphoma, sickle cell anemia and other life-threatening diseases, depend on a bone marrow or cord blood transplant (also called a BMT) to save their life. And there are millions of people on the Be The Match Registry® and registries throughout the world who stand ready to donate the cells needed for transplants for patients in need. This is the mission of Be The Match®. Be The Match

What is Lymphoma?

                               

Lymphoma is the name for a group of blood cancers that start in the lymphatic system or the Lymph nodes or glands. The lymphatic system is part of the body’s immune system – the body’s defense against infection. The marrow and lymphocytes are part of the immune system. Some other parts of the immune system are the lymph nodes, the lymphatic vessels, which connect the lymph nodes and contain lymph (a liquid that carries lymphocytes), and the spleen. Lymphoma generally starts in lymph nodes or lymphatic tissue in sites of the body such as the stomach or intestines. Lymphomas may involve the marrow and the blood in some cases.

Lymphoma is a type of blood cancer that occurs when lymphocytes–white blood cells that help protect the body from infection and disease–begin behaving abnormally. Abnormal lymphocytes may divide faster than normal cells or they may live longer than they are supposed to.

Because lymphatic tissue is in many parts of the body, Hodgkin lymphoma can start almost anywhere. Usually, it’s first found in a lymph node above the diaphragm, the thin muscle that separates the chest from the abdomen. But Hodgkin lymphoma also may be found in a group of lymph nodes. Sometimes it starts in other parts of the lymphatic system.

Lymphoma may develop in many parts of the body, including the lymph nodes, spleen, bone marrow, blood, or other organs. Hodgkin lymphoma begins when a lymphocyte (usually a B cell) becomes abnormal. The abnormal cell is called a Reed-Sternberg cell.

• Hodgkin lymphoma (HL) – There are five types of HL, an uncommon form of lymphoma that involves the Reed-Sternberg cells. The number of these cells increases as the disease advances.  Web Source

Nodular sclerosis Hodgkin lymphoma: This is the most common type of Hodgkin disease in developed countries. It is most common in teens and young adults, but it can occur in people of any age. It tends to start in lymph nodes in the neck or chest.

Mixed cellularity Hodgkin lymphoma: This is the second most common type and is seen mostly in older adults (although it can occur at any age). It can start in any lymph node but most often occurs in the upper half of the body.

Lymphocyte-rich Hodgkin lymphoma: This subtype usually occurs in the upper half of the body and is rarely found in more than a few lymph nodes.

Lymphocyte-depleted Hodgkin lymphoma: This is the least common form of Hodgkin disease. It is seen mainly in older people. It is more likely to be advanced when first found, in lymph nodes in the abdomen as well as in the spleen, liver, and bone marrow.

• Non-Hodgkin lymphoma (NHL) – There are more than 25 types of NHL, some of which are more common than others. Any lymphoma that does not involve Reed-Sternberg cells is classified as non-Hodgkin’s.

Subtypes of NHL  Web Source

B-cell lymphoma. About 90% of people in western countries with lymphoma have B-cell lymphoma.

T-cell lymphoma. About 10% of people with lymphoma have T-cell lymphoma. These 

lymphomas are more frequent in Asian countries.

NK-cell lymphoma. Less than 1% of people with lymphoma have NK-cell lymphoma.

NHL is also described by how quickly the cancer is growing, either “indolent” or “aggressive.” Indolent and aggressive NHL are equally common in adults. In children, aggressive NHL is more common.

• Indolent NHL. These types of lymphoma grow slowly. As a result, people with indolent NHL may not need to start treatment when it is first diagnosed. They are followed closely, and treatment is only started when they develop symptoms or the disease begins to change. This is called watchful waiting.
  When indolent lymphoma is located only in 1 or 2 adjacent areas, it is called localized disease (stages I and II, see the Stages section). For people with localized disease, radiation therapy may eliminate the NHL. However, most patients with indolent NHL have stage III or IV disease at the time of diagnosis. There are many effective treatments for these stages of indolent NHL. However, it may come back months or years after treatment has finished and require more treatment.
• Aggressive NHL. These types of lymphoma may develop rapidly, and treatment is usually started immediately. These types of lymphoma usually need more intensive chemotherapy. The doctor may recommend radiation treatment in addition to chemotherapy, especially in patients with limited stage disease (stage I or II). Many forms of aggressive lymphoma may be cured with effective treatment.

Some subtypes of lymphoma cannot easily be classified as indolent or aggressive. For example, mantle cell lymphoma (see below) has both indolent and aggressive NHL features.

Subtypes of NHL

In addition to determining if the NHL is indolent or aggressive and whether it is B-cell, T-cell, or NK-cell lymphoma, it is very important to determine the subtype of NHL. This is because each subtype can behave differently and may require different treatments. There are more than 60 NHL subtypes, although a number of them are quite rare. The most common subtypes are described below, along with some basic information about different treatments. Learn more in the Treatment Options section.

Distinguishing among the different subtypes of NHL can be difficult and requires pathologists or hematopathologists who are experts in the diagnosis of lymphoma. These specialists use sophisticated techniques and work closely with experienced oncologists. The diagnosis is based on how the lymphoma looks under the microscope. The doctors confirm the diagnosis with additional information from other tests, including tests of genetic material within the lymphoma cells. For more information on this process, see the Diagnosis section.

Subtypes of B-cell lymphoma

The most common subtypes of B-cell lymphoma are:

• Diffuse large B-cell lymphoma (DLBCL). This is the most common form of lymphoma. About 30% of NHL in the United States is this type. It is an aggressive form of NHL that involves organs other than the lymph nodes about 40% of the time. About 2 out of 3 people with DLBCL are cured with chemotherapy given in combination with rituximab (Rituxan). Radiation therapy is also used for some patients, especially if the lymphoma is found in a limited area. Your doctor may check the fluid around the brain, called cerebrospinal fluid (CSF), in certain cases at diagnosis and recommend treatments to prevent the lymphoma from spreading to the brain, called central nervous system (CNS) prophylaxis. However, most patients do not need this type of treatment.
  Recent research shows that there are different types of DLBCL, known as germinal center and non-germinal center. Research studies, called clinical trials, continue to look at whether patients should receive different types of treatment for these different types of DLBCL.
• Follicular lymphoma. This is the second most common form of lymphoma in the United States and Europe. About 20% of people with NHL have this subtype. It usually begins in the lymph nodes, is most often indolent, and grows very slowly. There is no known cure. However, recent studies show that more than 85% of patients live for at least 5 years after being diagnosed with follicular lymphoma. In addition, 50% of patients are estimated to live longer than 12 years. Patients with follicular lymphoma may receive a combination of chemotherapy; monoclonal antibodies, a type of targeted therapy; and/or radiation therapy. Or, they may be followed closely with watchful waiting and starting treatment only when symptoms appear.
  Recent clinical trials suggest that patients with follicular lymphoma have lived longer over the last few decades. Research shows that drugs such as bendamustine (Treanda) and lenalidomide (Revlimid), usually in combination with rituximab, are effective for this subtype. There are many new drugs being tested for use as part of first-line treatment for follicular lymphoma.
  Over time, follicular lymphoma may turn into DLBCL (see above), which will then require more aggressive treatment. This is called transformation. Stem cell transplantation, chimeric antigen receptor T-cells (CAR T-cells), and monoclonal antibody treatments may also be available treatment options, usually as part of clinical trials.
  Localized radiation therapy is often a common treatment choice for early-stage disease (stages I and II), but it may be combined with other treatments.
• Mantle cell lymphoma. About 5% to 7% of people with NHL have mantle cell lymphoma. It most often appears in people older than 60 and is much more common in men than in women. It usually involves the bone marrow, lymph nodes, spleen, and gastrointestinal system, which includes the esophagus, stomach, and intestines. Mantle cell lymphoma is identified by a protein called cyclin D1 or by a genetic change within the lymphoma cells involving chromosomes 11 and 14. Some patients have a slower-growing form of the disease that may be managed like follicular lymphoma (see above).
  The first approach to treating mantle cell lymphoma is to use a combination of chemotherapy and a monoclonal antibody. Most people with mantle cell lymphoma will have the disease return after finishing chemotherapy. As a result, doctors offer some patients high-dose chemotherapy followed by autologous stem cell transplantation at the end of their initial chemotherapy treatment, with the transplant often followed by maintenance therapy with the monoclonal antibody rituximab. Doctors may offer patients who do not have a stem cell transplant maintenance therapy with rituximab or other monoclonal antibody. Patients may also need radiation therapy to manage local symptoms.
  If chemotherapy does not work, there are differing opinions on the best way to treat mantle cell lymphoma. Research shows that drugs such as bortezomib (Velcade), ibrutinib (Imbruvica), and lenalidomide (Revlimid) may be effective treatments for this subtype. Researchers are studying these drugs as part of first-line treatment. Researchers are also studying new drugs for mantle cell lymphoma.
• Small lymphocytic lymphoma. This type of lymphoma is very closely related to a disease called B-cell chronic lymphocytic leukemia (CLL). About 5% of people with NHL have this subtype, which is considered indolent lymphoma. Patients with small lymphocytic lymphoma may receive a combination of chemotherapy and/or a monoclonal antibody. Or, they may be followed closely with watchful waiting. Stem cell transplantation, tumor vaccines, monoclonal antibody, or CAR T-cell treatments may also be available in clinical trials. Ibrutinib is now approved for patients who have had their disease return after initial treatment. Some patients can use ibrutinib as part of initial treatment, although this is still being studied.
• Primary mediastinal large B-cell lymphoma. This is an aggressive form of DLBCL (see above). It appears as a large mass in the chest area. The mass may cause breathing problems or superior vena cava (SVC) syndrome, a collection of symptoms caused by the partial blockage or compression of the superior vena cava. The superior vena cava is the major vein that carries blood from the head, neck, upper chest, and arms to the heart. Mediastinal large B-cell lymphoma is most common in women between 30 and 40 years old. About 2.5% of people with NHL have this subtype. Most often, doctors treat it with anthracycline-based chemotherapy plus rituximab. Depending on the chemotherapy regimen used, some patients also receive radiation therapy to the chest. Newer chemotherapy treatments may eliminate the need for radiation therapy in most patients. A closely related lymphoma called mediastinal grey-zone lymphoma (MGZL) may also occur in the same age group. It is approached in a manner similar to that of primary mediastinal large B-cell lymphoma.
• Splenic marginal zone B-cell lymphoma. This type of lymphoma begins in the spleen and can also involve the blood. It is usually slow growing, and the treatment approach is often watchful waiting. If a patient needs treatment, this type of lymphoma is often treated similarly to follicular lymphoma. Sometimes, the doctor may recommend surgical removal of the spleen.
• Extranodal marginal zone B-cell lymphoma of MALT. This type of lymphoma most commonly occurs in the stomach. However, it may also occur in the lung, skin, thyroid, salivary gland, or in the orbit and adjacent to the eye. Patients with this type of lymphoma sometimes have a history of autoimmune disease, such as lupus, rheumatoid arthritis, or Sjögren syndrome. When MALT occurs in the stomach, it is often successfully treated with antibiotics to treat an infection with Helicobacter pylori. This bacterium is causally related to the development of this lymphoma subtype. Other times, radiation therapy, surgery, chemotherapy, monoclonal antibodies, or a combination of these is the most common treatment plan. For disease in only 1 part of the body, radiation therapy can often cure MALT.
• Nodal marginal zone B-cell lymphoma. This rare type of indolent lymphoma involves the lymph nodes. About 1% of people with lymphoma have this subtype. In general, doctors treat this subtype of lymphoma similarly to follicular lymphoma (see above).
• Lymphoplasmacytic lymphoma. This is an indolent form of lymphoma, and 1% of people with NHL have this subtype. This form of lymphoma often involves the bone marrow, lymph nodes, and spleen. In many patients, this lymphoma produces proteins, called “M proteins,” that are found at high levels in the blood. When this occurs, the condition is called Waldenstrom’s macroglobulinemia (WM). Patients with WM sometimes have thickened blood, which may cause symptoms such as headache, blurry vision, dizziness, and shortness of breath. Treatment is similar to that for chronic lymphocytic leukemia or follicular lymphoma (see above). Treatment may include:
  • Watchful waiting
  • Chemotherapy
  • Targeted therapy with monoclonal antibodies
  • Combinations of chemotherapy and monoclonal antibodies
  • Ibrutinib
  Clinical trial researchers are studying using chemotherapy followed by stem cell transplantation as treatment option, which may be useful if the lymphoma returns after initial treatment.
• Primary effusion lymphoma. This rare and very aggressive form of lymphoma most often occurs in people:
  • Who have the human immunodeficiency virus (HIV), which causes autoimmune deficiency syndrome (AIDS)
  • Whose immune system does not work well for other reasons
  • Are elderly
  It begins as fluid around the lung, heart, or abdominal cavity. Often, there are no tumor masses. It is treated the same way as other diffuse large-cell lymphomas (see above).
• Burkitt lymphoma/Burkitt cell leukemia. This is a very rare and aggressive form of lymphoma. There are 3 forms of Burkitt lymphoma:
  • Endemic
  • Sporadic
  • Immunodeficiency-related lymphoma
  The endemic subtype occurs most commonly in Africa, appears most often in the jawbones of children, and is usually associated with infection with EBV. It can also be associated with HIV. In the United States, Burkitt lymphoma usually appears with a mass in the abdomen. Because this type of lymphoma spreads quickly, it needs immediate treatment. That treatment includes intensive chemotherapy, usually with treatment for the CNS to prevent it from spreading to the brain. This type of NHL is often curable with immediate treatment.

Subtypes of T-cell and NK-cell lymphoma

The most common subtypes of T-cell and NK-cell lymphoma are:

• Anaplastic large cell lymphoma, primary cutaneous type. This subtype of lymphoma only involves the skin. It is often indolent, although aggressive subtypes of the disease are possible. When the cancer is localized, radiation therapy is often effective. If it has spread, chemotherapy is the usual treatment. New drugs have recently been developed for the treatment of cutaneous lymphomas.
• Anaplastic large cell lymphoma, systemic type. This form makes up about 2% of all lymphomas and about 10% of all childhood lymphomas. In people with this subtype, an increased amount of the ALK-1 protein may be found in the cancer cells. Those who have ALK-1 protein in the cancer cells often have a better prognosis than those who have this subtype without the ALK-1 protein in the cell. It is an aggressive form of lymphoma, but chemotherapy often works well. New treatments, such as the monoclonal antibody brentuximab vedotin (Adcetris) or stem cell transplantation, may sometimes be a treatment option, especially for the subtype without the ALK-1 protein.
• Peripheral T-cell lymphoma, not otherwise specified (NOS). This is an aggressive form of lymphoma that is often advanced when doctors find it. It is most common in people older than 60 and makes up about 6% of all lymphomas in the United States and Europe. The cells of this lymphoma vary in size, and they have certain types of proteins, called CD4 or CD8, on their surface. It is treated with chemotherapy as with DLBCL (see above) or using other drugs. Researchers are studying many new drugs in clinical trials to treat this subtype. Stem cell transplantation may sometimes be an option.
• Angioimmunoblastic T-cell lymphoma. This is an aggressive form of lymphoma with specific symptoms:
  • Enlarged, often tender, lymph nodes
  • Fever
  • Weight loss
  • Rash
  • High levels of immunoglobulins in the blood
  Patients with angioimmunoblastic lymphoma have lowered immune systems, so infections are also common. Doctors identify this type of lymphoma by what it looks like under a microscope and by certain proteins found in the tumor cells. It is treated like other aggressive lymphomas.
• Adult T-cell lymphoma/leukemia (human T-cell lymphotropic virus type I positive). This type of lymphoma is caused by a virus called the human T-cell lymphotropic virus type I. It is an aggressive disease that often involves the bone and skin. Often, lymphoma cells are found in the blood, which is why this condition is sometimes also called leukemia. Chemotherapy does not usually work well for this form of lymphoma, although interferon and zidovudine (Retrovir) help some patients. Some patients experience remission, which is when symptoms go away for a period of time. Allogenic (ALLO) stem cell transplantation is the best approach for treatment of this type.
• Extranodal NK/T-cell lymphoma, nasal type. This is an aggressive type of lymphoma that is very rare in the United States and Europe but more common in Asian and Hispanic communities. It can occur in children or adults, most often involving the nasal area and sinuses. It can also involve the windpipe, gastrointestinal tract, skin, or a man’s testicles. Standard chemotherapy does not always work well for this type of NHL. That’s why combining radiation therapy with chemotherapy is an important addition to treatment when the disease is localized. Compared to other T-cell lymphomas, this subtype responds better to asparaginase (Elspar). This drug is now a standard part of initial treatment and is also used when this subtype of lymphoma comes back after treatment. Researchers are also studying stem cell transplantation for this type of lymphoma in clinical trials.
• Enteropathy-associated T-cell lymphoma. This type of lymphoma is rare in the United States but is more common in Europe. It is an aggressive form of T-cell lymphoma that involves the intestines of patients who have celiac disease or a history of gluten intolerance. Patients may receive high-dose chemotherapy to treat the disease.
• Gamma/delta hepatosplenic T-cell lymphoma. This is an aggressive form of peripheral T-cell lymphoma that involves the liver and spleen. The disease occurs most often in teenaged and young men. It is usually managed with chemotherapy followed by ALLO stem cell transplantation.
• Subcutaneous panniculitis-like T-cell lymphoma. This is a form of peripheral T-cell lymphoma that is similar to gamma/delta hepatosplenic T-cell lymphoma (see above). The disease involves the tissue under the skin and is often first diagnosed as panniculitis, which is inflammation of fatty tissues. It is treated as a high-risk aggressive lymphoma.
• Mycosis fungoides. This is a rare T-cell lymphoma that primarily involves the skin. It often has a very long and indolent course but may become more aggressive and spread to lymph nodes or internal organs. Radiation therapy, chemotherapy, or targeted therapy can help treat this form of NHL. Scientists have developed new drugs for the treatment of cutaneous lymphomas, some of which can be taken orally as a pill.

(web source) 

What Is Multiple Myeloma?

Multiple myeloma is a blood cancer related to lymphoma and leukemia. Though it can’t usually be cured, there are treatments that slow down its spread.

In multiple myeloma, a type of white blood cell called a plasma cell multiplies unusually. Normally, they make antibodies that fight infections. But in multiple myeloma, they release too much protein (called immunoglobulin) into your bones and blood. It builds up throughout your body and causes organ damage.

The plasma cells also crowd normal blood cells in your bones. They release chemicals that trigger other cells to dissolve bone. The weak areas of bone this creates are called lytic lesions.

As multiple myeloma gets worse, those plasma cells begin to spill out of your bone marrow and spread through your body. This causes more organ damage.

Causes

No one knows what causes multiple myeloma. But you’re more likely to get it if:

• You’re older than 65
• You’re African-American
• You have a family member with it

If you have one these other plasma cell diseases, you may be more likely to get multiple myeloma:

• Monoclonal gammopathy of undetermined significance (MGUS)
• Solitary plasmacytoma

Leukemia

Leukemia is a cancer of the early blood-forming cells. Most often, leukemia is a cancer of the white blood cells, but some leukemias start in other blood cell types. Leukemia is often described as being either acute (fast growing) or chronic (slow growing). Different types of leukemia have different treatment options and outlooks.Web Source

Acute lymphocytic leukemia (ALL), also called acute lymphoblastic leukemia, is a cancer that starts from the early version of white blood cells called lymphocytes in the bone marrow (the soft inner part of the bones, where new blood cells are made). Leukemia cells usually invade the blood fairly quickly. They can then spread to other parts of the body, including the lymph nodes, liver, spleen, central nervous system (brain and spinal cord), and testicles (in males). Other types of cancer also can start in these organs and then spread to the bone marrow, but these cancers are not leukemia. The term “acute” means that the leukemia can progress quickly, and if not treated, would probably be fatal within a few months. Lymphocytic means it develops from early (immature) forms of lymphocytes, a type of white blood cell. This is different from acute myeloid leukemia (AML), which develops in other blood cell types found in the bone marrow. For more information on AML, see Acute Myeloid Leukemia.  Other types of cancer that start in lymphocytes are known as lymphomas (non-Hodgkin lymphoma or Hodgkin disease). The main difference between these types of cancers is that leukemias like ALL mainly affects the bone marrow and the blood, and may spread to other places, while lymphomas mainly affect the lymph nodes or other organs but may involve the bone marrow. Sometimes cancerous lymphocytes are found in both the bone marrow and lymph nodes when the cancer is first diagnosed, which can make it hard to tell if the cancer is leukemia or lymphoma. If more than 25% of the bone marrow is replaced by cancerous lymphocytes, the disease is usually considered leukemia. The size of lymph nodes is also important. The bigger they are, the more likely the disease will be considered a lymphoma. For more information on lymphomas, see Non-Hodgkin Lymphoma and Hodgkin Disease. There are actually many types of leukemia. They differ based on what types of cells they start in, how quickly they grow, which people they affect, and how they are treated. To understand leukemia, it helps to know about the blood and lymph systems.

Acute myeloid leukemia (AML) has many other names, including acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, and acute non-lymphocytic leukemia. “Acute” means that this leukemia can progress quickly if not treated, and would probably be fatal in a few months. “Myeloid” refers to the type of cell this leukemia starts from. Most cases of AML develop from cells that would turn into white blood cells (other than lymphocytes), but some cases of AML develop in other types of blood-forming cells. The different types of AML are listed in How is Acute Myeloid Leukemia Classified? AML starts in the bone marrow (the soft inner part of certain bones, where new blood cells are made), but in most cases it quickly moves into the blood. It can sometimes spread to other parts of the body including the lymph nodes, liver, spleen, central nervous system (brain and spinal cord), and testicles. Other types of cancer can start in these organs and then spread to the bone marrow. But these cancers that start elsewhere and then spread to the bone marrow are not leukemias.

Chronic lymphocytic leukemia (CLL) is a type of cancer that starts from cells that become certain white blood cells (called lymphocytes) in the bone marrow. The cancer (leukemia) cells start in the bone marrow but then go into the blood. In CLL, the leukemia cells often build up slowly over time, and many people don't have any symptoms for at least a few years. In time, the cells can spread to other parts of the body, including the lymph nodes, liver, and spleen.

Chronic myeloid leukemia (CML), also known as chronic myelogenous leukemia, is a type of cancer that starts in certain blood-forming cells of the bone marrow. In CML, a genetic change takes place in an early (immature) version of myeloid cells - the cells that make red blood cells, platelets, and most types of white blood cells (except lymphocytes). This change forms an abnormal gene called BCR-ABL, which turns the cell into a CML cell. The leukemia cells grow and divide, building up in the bone marrow and spilling over into the blood. In time, the cells can also settle in other parts of the body, including the spleen. CML is a fairly slow growing leukemia, but it can also change into a fast-growing acute leukemia that is hard to treat. Most cases of CML occur in adults, but very rarely it occurs in children, too. In general, their treatment is the same as for adults. 

Chronic myelomonocytic leukemia (CMML) starts in blood-forming cells in the bone marrow and invades the blood. Cells in nearly any part of the body can become cancer and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

What Is Childhood Leukemia?  Web Source 

Cancer starts when cells start to grow out of control. Cells in nearly any part of the body can become cancer. To learn more about how cancers start and spread, see What Is Cancer? For information about the differences between childhood cancers and adult cancers, see Cancer in Children.

Leukemia is a cancer that starts in early blood-forming cells found in the bone marrow, the soft inner part of certain bones. Most often, leukemia is a cancer of the white blood cells, but some leukemias start in other blood cell types.

Any of the blood-forming cells from the bone marrow can turn into a leukemia cell. Once this change takes place, the leukemia cells no longer mature in a normal way. Leukemia cells might reproduce quickly, and not die when they should. These cells build up in the bone marrow, crowding out normal cells. In most cases, the leukemia cells spill into the bloodstream fairly quickly. From there they can go to other parts of the body such as the lymph nodes, spleen, liver, central nervous system (the brain and spinal cord), testicles, or other organs, where they can keep other cells in the body from doing their jobs.

Some other childhood cancers, such as neuroblastoma or Wilms tumor, start in other organs and can spread to bone marrow, but these cancers are not leukemia.

Normal bone marrow, blood, and lymphoid tissue

To understand the different types of leukemia, it helps to know about the blood and lymph systems.

Bone marrow

Bone marrow is the soft inner part of bones. New blood cells (red blood cells, white blood cells, and platelets) are made there. In infants, active bone marrow is found in almost all bones of the body, but by the teenage years it is found mainly in the flat bones (skull, shoulder blades, ribs, and hip bones) and vertebrae (the bones that make up the spine).

Bone marrow is made up of a small number of blood stem cells, more mature blood-forming cells, fat cells, and supporting tissues that help cells grow. Blood stem cells go through a series of changes to make new blood cells. During this process, the cells develop into 1 of the 3 main types of blood cell components.

Types of blood cells

Red blood cells carry oxygen from the lungs to all other tissues in the body, and take carbon dioxide back to the lungs to be removed. Having too few red blood cells in the body (anemia) can make you feel tired, weak, and short of breath because your body tissues are not getting enough oxygen.

Platelets are actually cell fragments made by a type of bone marrow cell called the megakaryocyte. Platelets are important in stopping bleeding by plugging up holes in blood vessels. Having too few platelets (thrombocytopenia) may cause you to bleed or bruise easily.

White blood cells help the body fight infections. Having too few white blood cells weakens your immune system and can make you more likely to get an infection.

Types of white blood cells

Lymphocytes are mature, infection-fighting cells that develop from lymphoblasts, a type of blood stem cell in the bone marrow. Lymphocytes are the main cells that make up lymphoid tissue, a major part of the immune system. Lymphoid tissue is found in the lymph nodes, thymus (a small organ behind the breast bone), spleen, tonsils and adenoids, and bone marrow. It is also scattered through the digestive system and respiratory system. There are 2 main types of lymphocytes:

• B lymphocytes (B cells) help protect the body against germs such as bacteria and viruses. They make proteins called antibodies that attach to the germ, marking it for destruction by other parts of the immune system.
• T lymphocytes (T cells) also help protect the body against germs. Some types of T cells destroy germs directly, while others play a role in either boosting or slowing the activity of other immune system cells.

Acute lymphocytic (lymphoblastic) leukemia (ALL), the most common type of childhood leukemia, develops from early forms of lymphocytes. It can start in either early B cells or T cells at different stages of maturity. Although both B cells and T cells can develop into leukemia, B-cell leukemias are much more common than T-cell leukemias. For more information, see the section “ How is childhood leukemia classified?”

Granulocytes are mature, infection-fighting cells that develop from myeloblasts, a type of blood-forming cell in the bone marrow. Granulocytes have granules that show up as spots under the microscope. These granules contain enzymes and other substances that can destroy germs, such as bacteria. The 3 types of granulocytes – neutrophils, basophils, and eosinophils – are distinguished under the microscope by the size and color of their granules.

Monocytes develop from blood-forming monoblasts in the bone marrow and are related to granulocytes. After circulating in the bloodstream for about a day, monocytes enter body tissues to become macrophages, which can destroy some germs by surrounding and digesting them. Macrophages also help lymphocytes recognize germs and start making antibodies to fight them.

Types of leukemia in children

Leukemia is often described as being either acute (fast growing) or chronic (slow growing). Almost all childhood leukemia is acute.

Acute leukemias

The main types of acute leukemia are:

• Acute lymphocytic (lymphoblastic) leukemia (ALL): About 3 out of 4 childhood leukemias are ALL. This leukemia starts from early forms of lymphocytes in the bone marrow.
• Acute myelogenous leukemia (AML): This type of leukemia, also called acute myeloidleukemia, acute myelocytic leukemia, or acute non-lymphocytic leukemia, accounts for most of the remaining cases. AML starts from the myeloid cells that form white blood cells (other than lymphocytes), red blood cells, or platelets.
• Hybrid or mixed lineage leukemia: In these rare leukemias, the cells have features of both ALL and AML. In children, they are generally treated like ALL and usually respond to treatment like ALL.

Both ALL and AML can be further divided into different subtypes. For more on these subtypes, see the section “ How is childhood leukemia classified?”

Chronic leukemias

Chronic leukemias are much more common in adults than in children. They tend to grow more slowly than acute leukemias, but they are also harder to cure. Chronic leukemias can be divided into 2 types. 

• Chronic myelogenous leukemia (CML): This leukemia rarely occurs in children. Treatment is similar to that used for adults (see “ Treatment of children with chronic myelogenous leukemia”). For more detailed information on CML, see Leukemia--Chronic Myeloid.
• Chronic lymphocytic leukemia (CLL): This leukemia is extremely rare in children. For more information on CLL, see Leukemia--Chronic Lymphocytic.

Juvenile myelomonocytic leukemia (JMML)

This rare type of leukemia is neither chronic nor acute. It begins from myeloid cells, but it usually doesn’t grow as fast as AML or as slow as CML. It occurs most often in young children (under age 4). Symptoms can include pale skin, fever, cough, easy bruising or bleeding, trouble breathing (from too many white blood cells in the lungs), and an enlarged spleen and lymph nodes. 

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