TAILIEUCHUNG - Chapter 105. Malignancies of Lymphoid Cells (Part 4)

The incidence of non-Hodgkin's lymphomas and the patterns of expression of the various subtypes differ geographically. T cell lymphomas are more common in Asia than in western countries, while certain subtypes of B cell lymphomas such as follicular lymphoma are more common in western countries. A specific subtype of non-Hodgkin's lymphoma known as the angiocentric nasal T/natural killer (NK) cell lymphoma has a striking geographic occurrence, being most frequent in Southern Asia and parts of Latin America. Another subtype of nonHodgkin's lymphoma associated with infection by human T cell lymphotropic virus (HTLV) I is seen particularly in southern Japan. | Chapter 105. Malignancies of Lymphoid Cells Part 4 The incidence of non-Hodgkin s lymphomas and the patterns of expression of the various subtypes differ geographically. T cell lymphomas are more common in Asia than in western countries while certain subtypes of B cell lymphomas such as follicular lymphoma are more common in western countries. A specific subtype of non-Hodgkin s lymphoma known as the angiocentric nasal T natural killer NK cell lymphoma has a striking geographic occurrence being most frequent in Southern Asia and parts of Latin America. Another subtype of nonHodgkin s lymphoma associated with infection by human T cell lymphotropic virus HTLV I is seen particularly in southern Japan and the Caribbean Chap. 181 . A number of environmental factors have been implicated in the occurrence of non-Hodgkin s lymphoma including infectious agents chemical exposures and medical treatments. Several studies have demonstrated an association between exposure to agricultural chemicals and an increased incidence in non-Hodgkin s lymphoma. Patients treated for Hodgkin s disease can develop non-Hodgkin s lymphoma it is unclear whether this is a consequence of the Hodgkin s disease or its treatment. However a number of non-Hodgkin s lymphomas are associated with infectious agents Table 105-4 . HTLV-I infects T cells and leads directly to the development of adult T cell lymphoma ATL in a small percentage of infected patients. The cumulative lifetime risk of developing lymphoma in an infected patient is . The virus is transmitted by infected lymphocytes ingested by nursing babies of infected mothers blood-borne transmission or sexually. The median age of patients with ATL is 56 years emphasizing the long latency. HTLV-I is also the cause of tropical spastic paraparesis a neurologic disorder that occurs somewhat more frequently than lymphoma and with shorter latency and usually from transfusion-transmitted virus Chap. 181 . Table 105-4 Infectious Agents Associated with

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