Epidemiology of Lymphoid Malignancy in Asia

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Abstract

Lymphoid malignancy is a remarkable disease because of its difference in epidemiology and etiology in different areas around the world.Several features of the epidemiology of lymphoid malignancy particularly stand out.The overall lymphoid malignancy incidence in Asian countries is relatively low.Histopathologic subtypes of lymphoma are different in eastern and western countries and generally similar among Asian countries.Differences in geographic distribution are striking for follicular lymphoma, which is less common in eastern countries than elsewhere.Asians have higher rates of aggressive NHL (Non-Hodgkin Lymphoma), T-cell lymphomas, and extra-nodal disease.Hodgkin's Lymphoma (HL) is relatively rare in Asian countries, and its subtypes are various in comparison with other areas.While for most cancers incidence and mortality are decreasing, the incidence rates of all subtypes of NHL have increased during the second half of the twentieth century, but the reason is poorly understood.This rise has been noted worldwide, in both genders, particularly in the elderly, and increase in high-grade NHL is predominant.Increase in NHL may be attributed to immunodeficiency, radiation, various infections, blood transfusion, familial aggregation, genetic susceptibility to NHL, chemical exposures to pesticides and solvents, and diet.Some studies also suggest that association between risk factors and specific NHL subtypes may be stronger than association between the same risk factors and NHL in aggregate.In addition the mentioned risk factors are different in various areas; therefore it may cause different distribution of lymphoid malignancy around the world.Geographic variation in lymphoma rate suggests the importance of environmental and gens effects.Risks for developing NHL include immunosuppression a causal link between infectious agents and lymphomagenesis, which have also been determined, particularly for human T-cell leukemia/lymphoma virus type1 (HTLV-1), Epstein-Barr virus (EBV), Helicobacter pylori infections and Hepatitis C Viruses (HCV)infection, which are relatively frequent in our area.In addition to the incidence of non-Hodgkin's lymphoma and its histological subtypes in Asian migrants to the United States which is lower in first-generation migrants, confirmed this suggestion.Other exogenous factors which have been implicated in lymphomagenesis, mentioned earlier, are used more without any protection in developing countries.They may play an important role in these differences.In this chapter we compare our findings with the data from other relevant studies available in literature from various parts of Asia, as well as with those of Western countries in an www.intechopen.comEpidemiology Insights 326 attempt to gain more insights into the differences between the Oriental and Western countries.In addition, because most different are related to etiologic factors, we also describe some of them. Non-Hodgkin LymphomaNon-Hodgkin lymphoma is a heterogeneous group of B-cell and T-cell neoplasm that arise primarily in the lymph nodes with varied clinical and biologic feature.Current classification system include the Revised European-American Lymphoma (REAL) classification and the World Health Organization (WHO) classification of hematopoietic and lymphoid neoplasms (Alexander, et al., 2007).The distribution of NHL types varies internationally (Anderson, Armitage, & Weisenburger, 1998).Epidemiological investigation of the NHL and its etiology may result in a better understanding and hence prevention. Descriptive epidemiologyBased on World Health Organization (WHO) classification,36 subtype of NHL (21 of B-cell and 15 of T-cell type) are recognized (Ekström-Smedby, 2006).NHL is the most common in the developed world, with the highest incidence in USA, Australia and New Zealand, and Europe, and the lowest in eastern and South central Asia (Ekström-Smedby, 2006).The age standardized incidence of NHL, around the year 2000, was estimated at approximately 10-14 per 100000 person-year in western countries, and 3 per 100000 in South central Asia (Parkin, Bray, Ferlay, & Pisani, 2005).In recent decades, there has been a dramatic increase in NHL incidence worldwide, of about 2-4% annually (Baris & Zahm, 2000).This increase has been occurred in both males and females in all age groups except the very young and in black and whites (Weisenburger, 1994).Racial differences have not been observed in age-specific incidence curves until the age of 45 for males and 35 for females, however over these ages, NHL develops more frequently in whites than blacks (Müller, Ihorst, Mertelsmann, & Engelhardt, 2005).The highest increase was observed in western countries, but this increase is no limited to these countries, and it has been observed in eastern countries such as India, Japan, Singapore (Devesa & Fears, 1992).Several reasons including: recategorisation of borderline type of lymphoma; less histopathological misdiagnosis of NHL as Hodgkin's disease; greater use of immunohistological techniques to examine cancer of uncertain cell type and coding effects, may account for part of the increase (A.J. Swerdlow, 2003).The general trends in western countries has been a dramatic increase in incidence in young men in areas where AIDS has become common (Morton, et al., 2006).The median age of NHL in Asian countries is significantly lower, compared to the population-based registration in western countries.The Hematological Malignancy Research Network reported that the median age of their patients was 68 years old (Smith, et al., 2010).However the median age in Asian countries is about 54 years old, in Iranian patients was 55 years old (Mozaheb, Aledavood, & Farzad, 2011), in the Korean patients 52 years (Y.-H. Ko, et al., 1998), in Taiwan 54 years (Lee, Tan, Feng, & Liu, 2005), and in a previous study in Japan 54.5 years (Aozasa, et al., 1985), but in a recent study in Japan it was 66 years (Aoki, et al., 2008).It is notable that the median age of Asian patients at the time of presentation was younger than in the western countries and it might be attributable to the

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