Definition: Leukemia, Lymphoma and Myeloma
Leukemia is cancer of the blood cells, usually affecting the white blood cells, which causes these cells to not work properly. There are four main types of leukemia.
Leukemia can occur in either the lymphoid or myeloid white blood cells. Cancer that develops in the lymphoid cells is called lymphocytic leukemia. Cancer that develops in the myeloid cells is called myelogenous leukemia. The disease can be either acute (begins abruptly and is usually short lived) or chronic (persists for a long period of time).
Acute leukemia involves new or immature cells, called blasts, which remain very immature and cannot perform their functions. The blasts increase in number rapidly, and the disease progresses quickly. In chronic leukemia, there are some blasts present, but they are more mature and can perform some of their functions. The cells grow more slowly so the disease progresses gradually.
Based on these findings, leukemia is then classified into one of the four main types of leukemias—acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), acute lymphocytic leukemia (ALL), or chronic lymphocytic leukemia (CLL). In addition to these, there are other types and subtypes of leukemia.
Scientists cannot explain why one person is more likely than another to get leukemia. Even so, researchers have found certain risk factors associated with the disease. A risk factor is anything that may increase a person’s chance for developing a disease. Exposure to large amounts of radiation seems to increase the risk of blood-related cancers, as well as exposure to certain chemicals over a long period of time. Certain genetic conditions, such as Down’s syndrome, may increase a person’s risk of leukemia. While little can be done to prevent the onset of this disease, people should limit, to the extent possible, their exposure to radiation and other chemicals over long periods of time.
Lymphoma is a type of cancer that originates in the lymphatic system. There are two main types of lymphoma. Hodgkin’s lymphoma, or Hodgkin’s disease, causes the cells in the lymphatic system to abnormally reproduce, eventually making the body less able to fight infection. All other types of lymphoma are called non-Hodgkin’s lymphomas. Cancers that spread to lymph nodes from other parts of the body are not lymphomas.
The lymphatic system, the tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases, includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels. It is important for filtering germs and cancer cells from various parts of the body. Lymphoid tissue is found in many places throughout the body, including lymph nodes, the thymus (found behind the chest bone and in front of the heart), the spleen (on the left side of the abdomen next to the stomach), the tonsils and adenoids, in the bone marrow, and scattered within other systems such as the digestive and respiratory systems.
While the exact causes of lymphoma are not fully understood, researchers have identified certain risk factors for the disease. A risk factor is anything that may increase a person’s chance of developing a disease. Risk factors for Hodgkin’s disease include the following:
- Infection with infectious mononucleosis
- Age—Hodgkin’s disease occurs most often in people between ages 15 and 34, and in people over the age of 55
- Gender—Lymphoma is more common in men than in women
- Family history of lymphoma, particularly brothers and sisters
- Epstein-Barr virus may increase a person’s risk of Hodgkin’s disease
- Acquired immune deficiency syndrome (AIDS)
Risk factors for non-Hodgkin’s lymphoma include:
- Genetic disease of the immune system
- Unprotected exposure to strong sunlight
- A high-fat, low-fiber diet
- Smoking or the use of tobacco products
- Excessive alcohol consumption
- Environmental factors such as radiation, chemicals, and infections
- Organ transplantation
- Infections with human immunodeficiency virus (HIV) or human T-cell leukemia/lymphoma virus (HTLV-1)
- Infections with malaria
- A history of infectious mononucleosis (caused by an infection with the Epstein-Barr virus)
- Helicobacter pylori (H. pylori) bacterium, which has been identified as a cause of stomach ulcers
Multiple myeloma is a type of cancer that affects certain white blood cells called plasma cells. Plasma cells are part of the immune system, which helps protect the body from infection and disease. Like all white blood cells, plasma cells begin their development in the bone marrow, the soft, spongy tissue that fills the center of most bones.
When cancer involves plasma cells, the body keeps producing more and more of these cells. The unneeded plasma cells—all abnormal and exactly alike—are called myeloma cells. Myeloma cells tend to collect in the bone marrow and in the hard, outer part of the bones. In most cases, the myeloma cells collect in various bones, often forming many tumors. When this happens, the disease is called multiple myeloma.
While scientists do not fully understand the causes of multiple myeloma, certain risk factors have been identified for the disease. A risk factor is anything that may increase a person’s chance for developing a disease. The risk factors for myeloma include:
- Age—Most myeloma patients are between 50 and 70 years old
- Race—The disease affects blacks more often than whites
- Gender—Men are more likely to develop myeloma than women
- A family history of myeloma
- Exposure to certain workplace chemicals and large amounts of radiation
In most cases, people who develop multiple myeloma have no clear risk factors. Scientists believe the disease may be the result of several factors (known and/or unknown) acting together.