Lymphomas develop in the cells of the lymphatic system. This scanning electron micrograph shows one of the primary cells of the lymphatic system, a T lymphocyte. T lymphocytes are specialized white blood cells that identify and destroy invading organisms such as bacteria and viruses. Some T lymphocytes directly destroy invading organisms, whereas other T lymphocytes regulate the immune system by directing immune responses. Cancers of the T lymphocytes, which comprise 15 percent of all lymphomas, spread through the lymphatic system to other parts of the body.
An estimated 62,000 Americans and almost 6,000 Canadians are diagnosed each year with lymphoma, also known as non-Hodgkin's disease, a group of related cancers involving the lymphatic system. The lymphatic system consists of many organs—including lymph nodes, the spleen, the tonsils and adenoids—and of cells in the bone marrow and in the digestive and respiratory systems. The main cell type found in the lymphatic system is the lymphocyte. There are two main types of lymphocytes, B lymphocytes (B cells) and T lymphocytes (T cells). Lymphomas develop in both types of lymphocytes—B-cell lymphomas make up 85 percent of all lymphoma cases, and T-cell lymphomas constitute the remaining 15 percent.
Lymphomas interfere with the function of healthy lymphocytes and spread to other organs in the body, where they compress and destroy healthy tissue. The most common symptom of lymphoma is a painless swelling in the lymph nodes in the neck, underarm, or groin. Other symptoms include fevers, night sweats, tiredness, weight loss, itching, and reddened patches on the skin. Sometimes there is nausea, vomiting, or abdominal pain.
Lymphoma risk increases with decreasing immune function, such as that caused by acquired immunodeficiency syndrome (AIDS) or exposure to certain infectious agents. Organ transplant recipients are also at higher risk because they take drugs that weaken the immune system as part of the transplantation process (see Medical Transplantation). The overall five-year survival rate for lymphoma in the United States is 51 percent, but people with less-severe tumors have a good chance of surviving longer than ten years.
Hodgkin’s disease, or Hodgkin’s lymphoma, is a less severe lymphoma diagnosed in approximately 7,000 Americans and 800 Canadians each year. Although the symptoms are similar to those of other lymphomas, the cancer cells in Hodgkin's disease look different under a microscope. Hodgkin’s disease is easier to treat than other types of lymphomas, a factor reflected in the five-year survival rate—more than 80 percent of people diagnosed with Hodgkin’s disease survive five years or longer.

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