**3. EBV-associated gastric carcinoma: the Americas' perspective**

Worldwide studies show higher EBVaGC prevalence in the Americas than in Asia [22]. These observations suggest a phylogeographic diversity of Epstein-Barr virus strains along with host and environmental associations [13]. In the Americas, the first report of gastric tumors positive for Epstein-Barr virus comes from Shibata and coworkers [23] (**Figure 3**). These authors, based on the histological resemblance between rare variant of undifferentiated gastric carcinomas with intense lymphoid infiltration (so-called lymphoepithelioma-like carcinoma [LELC]) and nasopharyngeal lymphoepithelioma, a well-established EBV-associated disease, detected EBV sequences in seven of eight LELC cases. EBV genomes were uniformly present only in carcinoma cells but not in reactive lymphoid infiltrate or normal gastric mucosa. Furthermore, the presence of a single genotype in each LELC cell was consistent with a clonal process, suggesting that EBV infection occurs before malignant transformation. Later, the same group expanded these findings to conventional gastric cancer, detecting EBV sequences in 22 of 138 (16%) cases [24]. In all these cases, the EBV genome was expressed, exclusively in gastric tumor cells. No EBV sequences were detected in surrounding lymphocytes, or precancerous lesions such as intestinal metaplasia and chronic gastritis. In addition, EBVaGC cases were most often detected in males than in females (p = 0.007). To define the clinicopathological characteristics of this novel molecular

**Figure 3.** A consolidated overview of EBVaGC in the Americas. Phylogeographic diversity of EBV strains along with host and environmental associations might explain the high incidence of EBVaGC in the Americas [24–31].

subtype of gastric cancer, a long-term, well-characterized cohort of Japanese-Americans living in Hawaii [32, 33] was evaluated. Unfortunately, beyond male predominance, no other clinicopathological characteristic, including survival, was found [32]. A high incidence of EBVaGC has been reported in Santiago, Chile, with 31 (16.8%) EBV-positive cases identified among 185 consecutive gastric cancer patients [25]. In this series, associations with the diffuse-type histology (p < 0.001) and nonantrum location (p = 0.01) were the most significant findings. Among Mexican descendants living in the USA, Gulley and coworkers and Vo and coworkers have reported 20 out of 138 (14.5%) EBVaGC cases [26, 27]. Interestingly, prevalence of EBV was 26.4% among Mexican descendants in comparison with 4.5% among white/ non-Hispanic cases. In addition, male predominance was found exclusively in those with Hispanic ancestry (p = 0.01) [27]. Koriyama et al. [28] examined 151 non–Japanese-Brazilian and 149 Japanese-Brazilian gastric carcinoma cases to identify an 11.2% prevalence among non–Japanese-Brazilian but only 4.7% among Japanese-Brazilian residents (p = 0.01). EBVassociated gastric carcinoma was predominant in males only in the non–Japanese-Brazilian cases (p = 0.047). Taken together, these findings suggest human phylogeographic diversity in the prevalence of EBVaGC.

**3. EBV-associated gastric carcinoma: the Americas' perspective**

12 Gastric Cancer

Worldwide studies show higher EBVaGC prevalence in the Americas than in Asia [22]. These observations suggest a phylogeographic diversity of Epstein-Barr virus strains along with host and environmental associations [13]. In the Americas, the first report of gastric tumors positive for Epstein-Barr virus comes from Shibata and coworkers [23] (**Figure 3**). These authors, based on the histological resemblance between rare variant of undifferentiated gastric carcinomas with intense lymphoid infiltration (so-called lymphoepithelioma-like carcinoma [LELC]) and nasopharyngeal lymphoepithelioma, a well-established EBV-associated disease, detected EBV sequences in seven of eight LELC cases. EBV genomes were uniformly present only in carcinoma cells but not in reactive lymphoid infiltrate or normal gastric mucosa. Furthermore, the presence of a single genotype in each LELC cell was consistent with a clonal process, suggesting that EBV infection occurs before malignant transformation. Later, the same group expanded these findings to conventional gastric cancer, detecting EBV sequences in 22 of 138 (16%) cases [24]. In all these cases, the EBV genome was expressed, exclusively in gastric tumor cells. No EBV sequences were detected in surrounding lymphocytes, or precancerous lesions such as intestinal metaplasia and chronic gastritis. In addition, EBVaGC cases were most often detected in males than in females (p = 0.007). To define the clinicopathological characteristics of this novel molecular

**Figure 3.** A consolidated overview of EBVaGC in the Americas. Phylogeographic diversity of EBV strains along with

host and environmental associations might explain the high incidence of EBVaGC in the Americas [24–31].

Among other countries in Latin America, Carrascal et al. [29], in Cali, Colombia, examined 178 consecutive gastric carcinoma cases identifying 23 (13%) cases of EBVaGCs. In this series, EBVaGC also revealed a male (p = 0.004) and nonantrum (p = 0.009) predominance. Herrera-Goepfert et al. [30] identified 24 of 330 (7.3%) cases in Mexico City. In this series, no male predominance was confirmed, although all cases were of diffuse-type histology. The lowest frequency reported in Latin America was in Peru, where 254 gastric cancer cases from Japanese descendants were evaluated by Yoshiwara et al. [31]. In this analysis, only 3.9% (10 cases) of EBV infection was found, with no male or histological subtype predominance detected. A consolidated overview of EBVaGC in the Americas is shown in **Figure 3**.

A recent meta-analysis estimated a prevalence of 11.49% (95% CI = 8.46–15.43), with high heterogeneity among the aforementioned studies (I2 = 73.3%; p < 0.001). Although heterogeneity for predominant sex, location and histology was low (I2 = 16.5% [p = 0.35], 0% [p = 0.68] and 33.7% [p = 0.16], respectively), these authors showed male predominance (p < 0.001) and diffuse-type histology (p < 0.001) as the most significant features of EBVaGC in the Americas (**Figures 4** and **5**) [13].

In Asia, low prevalence of EBV-associated gastric carcinoma has been described. The reported prevalence ranges from 6.1% in Northern China [34] to 9.1% in Southern China [35]. In Japan and Korea, the reported prevalence is 6.6 and 6.9%, respectively [35, 36]. Among European countries, Russia and the Republics of the former Soviet Union, 8.7% prevalence has been reported [37]. Interestingly, distribution of EBV-positive GCs by sex, site and histological type was similar to that in Japan. In a study carried out in Holland, EBV was detected in 7.2% of the gastric carcinomas from the Dutch D1D2 trial (N = 566; mean follow-up, 9 years) [38]. In France, only 5.8% of 85 cases of gastric adenocarcinomas were EBV-associated adenocarcinomas, from which 4 cases were of the intestinal histological type [39].

#### 14 Gastric Cancer

**Figure 4.** An estimated odds ratio (95% CI) for male predominance of EBV-associated gastric cancer in the Americas. Meta-analyses were performed by a random effects model with the inverse variance method, using the DerSimonian-Laird estimator, a logit transformation and the Clopper-Pearson confidence interval for individual studies. The results are shown in a log-scale. Taken from [4] with permission.

**Figure 5.** An estimated odds ratio (95% CI) for diffuse-type histology of EBV-associated gastric carcinoma in the Americas. Meta-analyses were performed by a random effects model with the inverse variance method, using the DerSimonian-Laird estimator, a logit transformation and the Clopper-Pearson confidence interval for individual studies. The results are shown in a log-scale. Taken from [13] with permission.
