Zahra Mozaheb

*Mashhad University of Medical Science Iran* 

### **1. Introduction**

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

Epidemiology of Lymphoid Malignancy in Asia 327

lower frequency of lymph node type lymphoma, and higher frequency of T-cell lymphoma,

Geographically related variation in the incidence of histopathologic distribution and clinical feature of NHL are well recognized (Shih & Liang, 1991). T-cell leukemia lymphoma occurs more frequently in southwest Japan, and the Caribbean basin (Takatsuki, 1990), northeast of Iran (Mashhad) (Abbaszadegan, et al., 2003); follicular lymphoma (FL) occurs less frequently in eastern countries (Intragumtornchai, et al., 1996; Mozaheb, et al., 2011; Ohshima, Suzumiya, & Kikuchi, 2002), and Immunoproliferative Small Intestinal Disease (IPSID) is the

Although B-cell lymphomas are constantly more common around the world, T-cell lymphomas are proportionally more common in Asia than in western countries (Müller, et al., 2005). Despite a higher percentage of T-cell lymphomas in Asians compared with westerns, the absolute incidences of T-NHL in HTLV1 non endemic areas, and western countries are quite similar when calculated by age-adjusted incidence (Aoki, et al., 2008; Au, et al., 2005; Wang, Young, Win, & Taylor, 2005). In a Chinese (non endemic area for HTLV1) study T-cell lymphoma proportion was 28.1% (Wang, et al., 2005), and also in Taiwan which is not endemic for HTLV1, T/NK lymphoma incidence was 12.4% (Lee, Tsou, Tan, & Lu, 2005). In an Indian study T-cell lymphomas formed 16.2% of the total NHL (Naresh, Srinivas, & Soman, 2000). Previous Japanese studies have reported a higher proportion of Tcell lymphoma, accounting for approximately 32-38% of non-Hodgkin lymphoma (Kadin, Berard, Nanba, & Wakasa, 1983; Pathologists, 2000), but the recent findings in Japan show the decreased frequency of T/NK cell lineage (25%) (Aoki, et al., 2008). In endemic area for HTLV1 in Japan, T/NK-cell neoplasm accounted for a higher percentage of lymphoid neoplasm, in Kyushu (30%) and Okinawa (38%), compared with other areas of Japan (18– 20%) (Aoki, et al., 2008). In one study in 1997 in Korea, in comparison with data reported in 1992, the proportion of T-lineage lymphoma was markedly decreased (25%). At that time, the T-lineage of lymphoma accounted for 35.2% of malignant lymphomas (Y. H. Ko, et al., 1998). It may be due to an increase in the frequency of B-cell lymphoma and an actual

most prevalent in the Middle east and Africa (Khojasteh & Haghighi, 1990).

decrease in T/NK-cell, but the real reason remains unclear (Y. H. Ko, et al., 1998).

**Diffuse Large B Cell Lymphoma***.* Among B-cell lymphomas, diffuse large B cell lymphoma (DLBCL) is the most common non-Hodgkin's Lymphoma representing approximately one third of all Non-Hodgkin's Lymphomas worldwide. This is one type of Non Hodgkin's Lymphoma in which the relative incidence does not seem to vary geographically (Mozaheb, et al., 2011). In almost all parts of the world this is the most frequent occurring non-Hodgkin's lymphoma (K. E. Hunt & Reichard, 2008). In some studies like a recent study in Mashhad, Iran (Mozaheb, et al., 2011) there was a higher rate of aggressive NHL specially, diffuse large B cell lymphoma which occurs more frequent than others. It may be related to the etiology of diffuse large B cell lymphoma such as immune deficient conditions and their treatments which in most instances caused aggressive non-Hodgkin's lymphoma, and we should consider that a comparative excess of DLBCL resulting in a deficit of follicular lymphoma. In addition genetic factors may have an important role in this difference.

**2.1.2 Histological subtype of non-Hodgkin's lymphoma** 

**2.1.1 Immunologic characterization of non-Hodgkin's lymphoma** 

which comes as follows.

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**.** 
