There are two main types of lymphocytes: B lymphocytes (B-cells) and T lymphocytes (T-cells). Normal, healthy B-cells produce antibodies that guide the immune system in fighting and killing harmful bacteria. Normal, healthy T-cells recognize and destroy virus-infected or cancer cells. They also can release substances called cytokines that attract other types of white blood cells, which then digest the infected cells. In an organ transplant, it is the T-cells that must be suppressed so they do not attack the new organ, causing the body to reject it.
Non-Hodgkin's lymphoma (NHL) occurs with the malignant (cancerous) growth of B or T cells. Although both types can develop into lymphomas, B-cell lymphomas are much more common, accounting for 85% of all cases of NHL compared to T-cell lymphomas, which account for 15% of all cases of NHL, according to the American Cancer Society.
There are over 29 different types of NHL, each differentiated by the type of cancer cell. Some scientists classify cells by growth rate: indolent refers to slow growth and aggressive refers to fast-growing cells. Some also classify NHLs by cell type: T-cell, large cell, B-cell and follicular cell, etc.. For a more complete listing of lymphoma types, please see the Lymphoma Information Network's classification and typing page at www.lymphomainfo.net/nhl/classify.html.
What causes NHL?
Anything that can increase the chance of contracting lymphoma is considered a risk factor. This may be lifestyle-related, environmental or genetic (inherited) factors.
While risk factors for some cancers include extended exposure to strong sunlight without protection, a high-fat, low-fiber diet, smoking, and excessive alcohol consumption, none of these strongly affect a person's risk of developing NHL.
Children born with abnormal or deficient immune systems have an increased chance of developing NHL during childhood or as young adults. While some of these immune deficiencies may be inherited and passed on to children, NHL survivors do NOT pass an increased risk of cancer on to their children.
There has been recent progress in understanding how DNA may play a part in causing normal lymphocytes to become cancerous. Cancers can be caused by DNA defects (mutations) which cause genes that direct cell growth (oncogenes) to overproduce or genes that slow growth or promote cell death (tumor surpressor genes) to fail. Some DNA mutations can be inherited, increasing a risk for certain types of cancer but NHL is NOT one of the cancers caused by these inherited gene mutations.
NHL-related DNA mutations are usually acquired after birth and often appear for no apparent reason though some may result from lifestyle (cancer-causing drug exposure) or environmental (radiation exposure) risk factors. When a cell divides, its DNA is duplicated and if an exact copy of the DNA is not produced, the "mistake" cells may slip past the body's repair efforts and continue to divide and grow, producing cancerous cells.
Unfortunately, the bottom line is that most patients with NHL have no known risk factors, therefore the true cause of non-Hodgkin's lymphoma is still unknown. However, it is important to note that NHL is NOT contagious so patients pose no health risk to others at any time and possessing a risk factor does not mean a person will develop NHL.
Some facts and figures according to the American Cancer Society
Since most people with NHL have no known risk factors, there is no way to prevent lymphomas from developing. By working to prevent the significant known risk factor, HIV, we are able to reduce the chances of developing lymphomas but not prevent them entirely.
With respect to chemotherapy and radiation treatments, both of which compromise the immune system and increase a risk for developing NHL, doctors are currently studying alternative methods of treating cancers that reduce the risk of NHL. However, the life-threatening impact of the diseases successfully treated through chemotherapy and radiation and the immediate life savings of organ transplantation must be balanced against the potential risk of developing NHL later in life.
Treatment depends on the stage and grade of the lymphoma. The grade determines how rapidly it is likely to grow; stage determines how far the disease has progressed. Grades are determined by examination of a tissue sample under a microscope. However, the specific type of lymphoma or part of the body affected by the disease may play an even greater part in determining treatment protocol.
Surgery may be used to obtain tissue samples for diagnosis and classification of lymphoma but it is rarely used to treat NHL unless the cancer is localized to certain organs. The most common treatment is chemotherapy. If the cancer is localized, radiation also may be used in conjunction with chemotherapy. Some types of very advanced and non-responsive lymphomas may call for bone marrow or stem cell transplants but not in all cases. Monoclonal antibodies also are becoming more and more available and can be effective in fighting very specific types of cancer. This treatment is generally used for patients whose NHL has either not responded to chemotherapy or has relapsed. Clinical trials are now being held on the effectiveness of monoclonal antibodies. Some doctors prescribe a "watch and wait" pattern whereby they may halt treatment for a period of time to see how an indolent (slow growth or almost dormant) lymphoma is going to progress in order to determine the best course of treatment
For specific details on how the stages, grades and cancer locations may determine an individual's treatment plan, please visit the American Cancer Society's site on the treatment of non-Hodgkin's lymphoma at www3.cancer.org/cancerinfo/load_cont.asp?ct=32.
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