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The prognostic effect of ethnicity for gastric and esophageal cancer: the population-based experience… Bashash, Morteza; Hislop, T G; Shah, Amil M; Le, Nhu; Brooks-Wilson, Angela; Bajdik, Chris D May 9, 2011

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RESEARCH ARTICLE Open AccessThe prognostic effect of ethnicity for gastricand esophageal cancer: the population-basedexperience in British Columbia, CanadaMorteza Bashash1,2, T Greg Hislop1,6, Amil M Shah3,5, Nhu Le1,7, Angela Brooks-Wilson4,8 and Chris D Bajdik1,6*AbstractBackground: Gastric and esophageal cancers are among the most lethal human malignancies. Their epidemiologyis geographically diverse. This study compares the survival of gastric and esophageal cancer patients amongseveral ethnic groups including Chinese, South Asians, Iranians and Others in British Columbia (BC), Canada.Methods: Data were obtained from the population-based BC Cancer Registry for patients diagnosed with invasiveesophageal and gastric cancer between 1984 and 2006. The ethnicity of patients was estimated according to theirnames and categorized as Chinese, South Asian, Iranian or Other. Cox proportional hazards regression analysis wasused to estimate the effect of ethnicity adjusted for patient sex and age, disease histology, tumor location, diseasestage and treatment.Results: The survival of gastric cancer patients was significantly different among ethnic groups. Chinese patientsshowed better survival compared to others in univariate and multivariate analysis. The survival of esophagealcancer patients was significantly different among ethnic groups when the data was analyzed by a univariate test(p = 0.029), but not in the Cox multivariate model adjusted for other patient and prognostic factors.Conclusions: Ethnicity may represent underlying genetic factors. Such factors could influence host-tumorinteractions by altering the tumor’s etiology and therefore its chance of spreading. Alternatively, genetic factorsmay determine response to treatments. Finally, ethnicity may represent non-genetic factors that affect survival.Differences in survival by ethnicity support the importance of ethnicity as a prognostic factor, and may provideclues for the future identification of genetic or lifestyle factors that underlie these observations.BackgroundGastric and esophageal cancers are among the mostlethal human malignancies. Worldwide, gastric cancer isthe fourth most common cancer, but the second mostcommon cause of death from cancer [1]. Esophagealcancer is the eighth most common cancer, but the sixthmost common cause of cancer death [1]. The epidemiol-ogy of these cancers is geographically diverse. Incidencerates for gastric cancer vary from 3.4 per 100,000among women in North America to 26.9 per 100,000among men in Asia. The 5-year survival is usually about20% [2]; however, countries with higher incidence ratesof gastric cancer generally have better survival ratesthan countries with lower incidence [3]. Incidence ratesfor esophageal cancer range from 5-10 per 100,000 inNorth America to more than 100 per 100,000 in EasternIran near the Caspian Sea [4]. The differences betweenpopulations reflect environmental and lifestyle (includ-ing healthcare) factors, as well as genetic profiles [5].In order to investigate risk associated with geneticcharacteristics of a population (ie. ethnicity) and toreduce or eliminate environmental confounding, it ispreferable to conduct a study in a single geographic areawith a heterogenous population rather than to conductinternational comparisons [5]. British Columbia (BC),Canada, has a multi-ethnic population. Based on 2006census data, about one in every four of the 4,428,400British Columbians (24.8%) belongs to a visible minority,representing about one million people in the province.Visible minority is a category that includes persons who* Correspondence: cbajdik@bccrc.ca1Cancer Control Research Program, BC Cancer Agency, Vancouver, CanadaFull list of author information is available at the end of the articleBashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164© 2011 Bashash et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.are non-Caucasian in race or non-white in colour andwho do not report being Aboriginal http://www.statcan.gc.ca/concepts/definitions/minority01-minorite01a-eng.htm. Of these, approximately 75% were born outsideCanada, and about 60% immigrated to BC from 1991 to2006 [6]. That indicates about 676,000 immigrants and297,000 non-immigrants in BC belonged to a visibleminority group in 2006 [6]. Chinese was the largestgroup, accounting for 40% of all visible minorities in theprovince, followed by South Asians (26%) [6]. Iraniansrepresent a relatively small but growing percentage ofthe BC population (0.5%, or 19,000 people) in 2001 [7],although they originate from a geographic region withthe world’s highest incidence of gastric and esophagealcancers [8,9]. This study compares survival of gastricand esophageal cancer patients among Chinese, SouthAsian and Iranian and other ethnic groups in BC.MethodsThis study received approval from the Research EthicsBoard at the BC Cancer Agency (BCCA). The studyuses historical patient records and, accordingly, patientswere not re-contacted. Cancer incidence and survivaldata for invasive primary esophageal and gastric cancerswere obtained from the population-based BC CancerRegistry (BCCR) for all BC patients diagnosed between1984 and 2006. The BCCR receives national informationregarding the vital status of patients and is updatedaccordingly. The topology and histology of cases werecoded according to the International Classification ofDiseases for Oncology, Third Edition (ICD-O) [10] forgreater coherence with registry information recordedduring the entire study time period. The topography foresophageal cancers was then grouped into four cate-gories: esophagus upper third (ICD-O codes C15.0-C15.3), esophagus middle third (ICD-O codes C15.4),esophagus lower third and overlapping lesions (ICD-Ocodes C15.5), and esophagus unknown (ICD-O codesC15.8 and C15.9). The topography for gastric cancerwas grouped into three categories: proximal third (car-dia) in the gastroesophageal junction or upper third ofthe stomach (ICD-O codes C16.0 and C16.1), distal sto-mach or lower two thirds of the stomach (ICD-O codesC16.2-C16.7), and unknown or unspecified/overlappinglesion (ICD-O codes C16.8 and C16.9). Histologicalcategories for esophageal cancers were squamous cellcarcinoma (ICD-O codes 8050-8082), adenocarcinoma(ICD-O codes 8140-8573) and others (mainly ICD-Ocodes 8000-8020). Histology for gastric cancer was alsocategorized based on the Lauren classification system asdiffuse or intestinal type [11] (diffuse gastric tumorsdefined by histology codes 8142, 8145 and 8490) [12].For both esophageal and gastric cancers, nonepithelialtumors (ICD-O codes 8800-9759) were excluded.Primary treatment was categorized as surgery, che-motherapy and radiotherapy, with only therapeutic (i.e.,not diagnostic) surgeries being considered as treatment.Some patients received more than one type of primarytreatment, but other information, including informationabout adjuvant therapy and individual hospitalsattended, was not available. Overall survival was the pri-mary study outcome, and was calculated as the timebetween diagnosis and death. Complete follow-up infor-mation was available for all patients to 31 August 2007.The ethnicity of patients was determined according totheir names and categorized as Chinese, South Asian orIranian. This method for identification of ethnicity wasnecessary because the BCCR does not record ethnicityor place of birth. Two sources were used to generatesurname listings for each of the three ethnic groups:local telephone directories and the Screening Mammo-graphy Program of BC (SMPBC; a population-basedscreening program serving nearly 50% of the age-eligiblefemale population in BC) database. The names in localtelephone directories were reviewed manually to identifyChinese, South Asian and Iranian surnames; this wasdone by several members of the research team fromeach of the respective ethnic groups. In addition, sincethe SMPBC database retains both ‘place of birth’ and‘ethnic group’ as reported by the client, all surnameswere listed from this source for Chinese women report-ing ‘Chinese’ as their ethnicity, South Asian womenreporting ‘India’, and Iranian women reporting ‘Iran’.The same members of the research team reviewed thesesurname listings and eliminated names that were nottypically Chinese, South Asian or Iranian, or which werecommon to other population groups. This method toidentify ethnicity has been used in a number of otherstudies [7,13-16]] and the methodology has been dis-cussed elsewhere [17-19]. Patients not classified asbelonging to any of these three ethnic groups were cate-gorized as “Other.” Based on the ethnic distribution ofthe BC population, more than 80% of “Other” are Brit-ish and Western Europeans [20]. British and WesternEuropeans could not be separated as a group becausecorresponding name lists do not exist.Univariate comparisons of demographic, tumor andtreatment variables between ethnic groups were per-formed using Chi-square tests. Survival was calculatedusing the Kaplan-Meier method and log-rank tests wereused to compare survival differences among groups. Allanalyses were performed separately for non-metastatic(Stage I-III) and metastatic (Stage IV) disease. Cox pro-portional hazards regression was used to estimate theeffect of ethnicity adjusted for patient sex, age (less than55 years, 55-64 years, 65-74 years and 75+ years), dateof diagnosis (1984-1990, 1991-1995, 1996-2000, 2001-2006), tumor histology (intestinal and diffuse for gastricBashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 2 of 8cancer; adenocarcinoma and squamous cell carcinomafor esophageal cancer), tumor location, disease stageand primary treatment received (surgery, radiotherapyand/or chemotherapy). The hazard ratio (HR) was calcu-lated for each ethnic group and is the ratio of thehazard rate in each ethnic group compared to the“Other” group. For each HR, a 95% confidence interval(95%CI) was calculated. p-values less than 0.05 wereconsidered statistically significant.ResultsGastric cancer3136 cases of invasive gastric cancer were diagnosedduring the study period. Descriptive information for thecases is shown by ethnicity in Table 1. The age and sexdistributions were significantly different among the eth-nic groups (p < 0.01). A higher proportion of Chineseand South Asian gastric cancer patients were female ascompared to the other ethnic groups. The average ageat diagnosis was 61.0 years for Iranians, 62.6 years forChinese, 61.7 years for South Asians, and 65.4 years forOther ethnicities. There were significant differencesamong the year of diagnosis by ethnicity (p < 0.01).Tumor location was significantly different among theethnic groups (p < 0.01). Tumors in the proximal 1/3 ofthe stomach were more common in South Asians andOther ethnicities as compared to Chinese and Iranians.Histology based on the Lauren classification was alsosignificantly different among ethnic groups (p = 0.03).The diffuse type of gastric cancer was most commonamong Chinese compared to the other ethnic groups.The distribution of stage and proportion with metastaticdisease was not significantly different among the ethnicgroups; however, treatment by surgery and chemother-apy were significantly different among the ethnic groups.The Chinese and Iranian groups received surgery moreoften than people in the South Asian or Other groups(p < 0.01), and the South Asian and Iranian groupsreceived chemotherapy more often than Chinese orOthers (p < 0.01). Among treated groups; 61% of Ira-nians, 47% of Chinese, 54% of South Asians and 41% ofOthers received more than one type of primaryTable 1 Descriptive characteristics for gastric cancer by ethnicityIranian Chinese South Asian Other pSex (N = 3136) Male 15 (78.9%) 168 (62.2%) 57 (58.8%) 1974 (71.8%) p < 0.001Female 4 (21.1%) 102 (37.8%) 40 (41.2%) 776 (28.2%)Age in years (N = 3136) Less than 55 7 (36.8%) 86 (31.9%) 26 (26.8%) 515 (18.7%) p < 0.00155-64 3 (15.8%) 49 (18.1%) 20 (20.6%) 652 (23.7%)65-74 7 (36.8%) 65 (24.1%) 35 (36.1%) 884 (32.1%)75 and More 2 (10.5%) 70 (25.9%) 16 (16.5%) 699 (25.4%)Years of Diagnosis (N = 3136) 1984-1990 0 (0.0%) 32 (11.9%) 11 (11.3%) 643 (23.4%) p < 0.0011991-1995 7 (36.8%) 54 (20.0%) 16 (16.5%) 481 (17.5%)1996-2000 4 (21.1%) 63 (23.3%) 27 (27.8%) 626 (22.8%)2001-2006 8 (42.1%) 121 (44.8%) 43 (44.3%) 1000 (36.4%)Tumor Histology - Lauren classification (N = 3136) Intestinal 14 (73.7%) 205 (75.9%) 74 (76.3%) 2188 (79.6%) 0.032Diffuse 3 (15.8%) 55 (20.4%) 13 (13.4%) 382 (13.9%)Other 2 (10.5%) 10 (3.7%) 10 (10.3%) 180 (6.5%)Tumor Location (N = 3136) Proximal 1/3 6 (31.6%) 52 (19.3%) 47 (48.5%) 1302 (47.3%) p < 0.001Distal 2/3 10 (52.6%) 171 (63.3%) 28 (28.9%) 894 (32.5%)NES/NOS* 3 (15.8%) 47 (17.4%) 22 (22.7%) 554 (20.1%)Tumor Stage (N = 2567) I 1 (5.6%) 14 (6.1%) 3 (3.7%) 108 (4.8%) 0.85II 6 (33.3%) 65 (28.5%) 29 (35.8%) 702 (31.3%)III 6 (33.3%) 96 (42.1%) 29 (35.8%) 829 (37.0%)IV 5 (27.8%) 53 (23.2%) 20 (24.7%) 601 (26.8%)Surgery (N = 3080) Yes 14 (73.7%) 178 (66.7%) 56 (57.7%) 1502 (55.7%) 0.0027No 5 (26.3%) 89 (33.3%) 41 (42.3%) 1195 (44.3%)Chemotherapy (N = 3065) Yes 10 (52.6%) 116 (43.6%) 44 (45.4%) 906 (33.8%) p < 0.001No 9 (47.4%) 150 (56.4%) 53 (54.6%) 1777 (66.2%)Radiotherapy (N = 3058) Yes 6 (31.6%) 99 (37.1%) 43 (44.3%) 1203 (45.0%) 0.061No 13 (68.4%) 168 (62.9%) 54 (55.7%) 1472 (55.0%)* NES not elsewhere specified; NOS not otherwise specified.Bashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 3 of 8treatment (ie., Surgery+Chemotherapy+Radiotherapy,Surgery+Chemotherapy, Surgery+Radiotherapy or Che-motherapy+Radiotherapy). Each type of primary treat-ment was included as a separate variable in multivariatemodels. Iranians had a median survival of 20 months(95%CI; 10.6-29.4), Chinese had a median survival of16 months (95%CI; 12.5-19.1), South Asians had a med-ian survival of 15 months (95%CI; 11.2-18.1) and Othershad a median survival of 10 months (95%CI; 9.4-10.7).Figure 1 shows survival curves for gastric cancerpatients according to ethnic group. Survival was signifi-cantly different between ethnic groups (p < 0.01).Iranians (HR = 0.62, 95%CI; 0.31-0.96), South Asians(HR = 0.87, 95%CI; 0.59-0.94) and Chinese (HR = 0.77,95%CI; 0.61-0.81) showed better survival than people inthe Other category. When considered separately bypresence or absence of metastatic disease, statisticallysignificant differences were only found for non-meta-static disease (p < 0.01), as shown in Figure 2. SouthAsians (HR = 0.72, 95%CI; 0.54-0.97) and Chinese(HR = 0.64, 95%CI; 0.53-0.76) showed better survivalthan the Other category. The survival of Iranians (HR= 0.50, 95%CI; 0.24-1.04) was also better than peoplein the Other category, but the small number of Ira-nians (and wide confidence interval) does not excludethe possibility that this is due to chance. Furthermore,the association between survival and ethnicity was onlysignificant for patients with non-metastatic diseasewho received therapeutic surgery (p < 0.01), as shownin Figure 3.In multivariate analyses adjusting for patient factors,disease factors and treatment, there was an overall sig-nificant difference among ethnic groups. For individualethnic groups, only Chinese had significantly longer sur-vival than the Other ethnicities, as shown in Table 2.This survival advantage in Chinese was only seen fornon-metastatic disease (HR = 0.78, 95% CI; 0.64-0.95).Esophageal cancer2873 cases of esophageal cancer were diagnosed duringthe study period. Descriptive characteristics of thesepatients are presented by ethnicity in Table 3. Themajority of South Asians were women whereas themajority in the other ethnic groups were men (p <0.01). There was no significant difference in age at diag-nosis among the ethnic groups, the average age being73.0 years, 68.0 years, 65.5 years and 68.4 years for Ira-nians, Chinese, South Asians and Other ethnicities,respectively. There was no significant difference amongethnic groups based on date of diagnosis.Figure 1 Survival of gastric cancer patients by ethnic group.Figure 2 Survival of gastric cancer patients by ethnic group fornon-metastatic disease.Figure 3 Survival of gastric cancer patients who receivedsurgery by ethnic group for non-metastatic disease.Bashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 4 of 8Tumour location was significantly different amongethnic groups (p < 0.01). More than half of tumors inIranians and Other ethnicities were located lower thirdof the esophagus whereas this location was less commonin Chinese and South Asians. Histology was significantlydifferent among the ethnic groups (p < 0.01), withChinese and South Asians having higher proportions ofsquamous cell carcinoma compared to Iranians andOther ethnicities.There were no significant differences in stage or theproportion with metastatic disease among ethnic groups.Treatment received was not different, except for che-motherapy which had significant differences among theethnic groups (p < 0.01), with the Chinese, Iranian andSouth Asian patients accessing chemotherapy moreoften than Other ethnicities. 15% of Iranians, 45% ofChinese, 46% of South Asians and 42% of people in theOther category received more than one type of primarytreatment. Iranians had median survival of 7 months(95%CI; 2.1-11.9), Chinese had a median survival of 10months (95%CI; 7.0-12.9), South Asians had a mediansurvival of 9 months (95%CI; 6.9-11.1) and people in theOther category had a median survival of 8 months (95%CI; 7.6-10.6). Figure 4 shows the survival curves forTable 2 Effect size of ethnicity for overall survival ofgastric cancer patientsEthnicity N HR 95% CI pIranian 16 0.64 0.34 1.18 P = 0.006Chinese 214 0.76 0.65 0.90South Asian 72 0.88 0.68 1.14Other 2038 ReferenceHazard ratio (HR) and 95% confidence interval (CI) from Cox proportionalhazards regression analysis adjusted for patient sex, patient age, year ofdiagnosis, tumor histology (Lauren), tumor location, tumor stage andtreatment.Table 3 Descriptive characteristics for esophageal cancer by ethnicityIranian Chinese South Asian Other PSex (N = 2873) Male 10 (71.4%) 94 (74.6%) 57 (47.9%) 1821 (69.7%) p < 0.001Female 4 (28.6%) 32 (25.4%) 62 (52.1%) 793 (30.3%)Age in years (N = 2873) Less than 55 0 (0.0%) 14 (11.1%) 21 (17.6%) 314 (12.0%) 0.1255-64 1 (7.1%) 35 (27.8%) 32 (26.9%) 610 (23.3%)65-74 9 (64.3%) 41 (32.5%) 35 (29.4%) 858 (32.8%)75 and More 4 (28.6%) 36 (28.6%) 31 (26.1%) 832 (31.8%)Years of Diagnosis (N = 2873) 1984-1990 3 (21.4%) 16 (12.7%) 22 (18.5%) 486 (18.6%) 0.1641991-1995 1 (7.1%) 26 (20.6%) 15 (12.6%) 580 (22.2%)1996-2000 3 (21.4%) 38 (30.2%) 33 (27.7%) 637 (24.4%)2001-2006 7 (50%) 46 (36.5%) 49 (41.2%) 911 (34.9%)Tumor Histology (N = 2873) SCC * 5 (35.7%) 103 (81.7%) 81 (68.1%) 1389 (53.1%) p < 0.001AC ** 7 (50.0%) 19 (15.1%) 27 (22.7%) 1101 (42.1%)Other 2 (14.3%) 4 (3.2%) 11 (9.2%) 124 (4.8%)Tumor Location (N = 2873) Upper 1/3 2 (14.3%) 23 (18.3%) 17 (14.3%) 314 (12.0%) p < 0.001Middle 1/3 1 (7.1%) 45 (35.7%) 34 (28.6%) 605 (23.1%)Lower 1/3 9 (64.3%) 40 (31.7%) 51 (42.9%) 1383 (52.9%)NES/NOS*** 2 (14.3%) 18 (14.3%) 17 (14.3%) 312 (12.0%)Tumor Stage (N = 2594) I 1 (8.3%) 12 (10.3%) 8 (7.6%) 212 (9.0%) 0.84II 6 (50.0%) 66 (56.9%) 56 (53.3%) 1363 (57.8%)III 3 (25.0%) 27 (23.3%) 26 (24.8%) 459 (19.4%)IV 2 (16.7%) 11 (9.5%) 15 (14.3%) 326 (13.8%)Surgery (N = 2830) Yes 2 (15.4%) 24 (19.2%) 35 (29.9%) 630 (24.5%) 0.23No 11 (84.6%) 101 (80.8%) 82 (70.1%) 1944 (75.5%)Chemotherapy (N = 2820) Yes 0 (0.0%) 39 (31.2%) 25 (21.6%) 526 (20.5%) 0.0084No 13 (100.0%) 86 (68.8%) 91 (78.4%) 2039 (79.5%)Radiotherapy (N = 2853) Yes 13 (100.0%) 112 (89.6%) 111 (93.3%) 2240 (86.3%) 0.052No 0 (0.0%) 13 (10.4%) 8 (6.7%) 355 (13.7%)*SCC squamous cell carcinoma.**AC adenocarcinoma.*** NES not elsewhere specified; NOS not otherwise specified.Bashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 5 of 8esophageal cancer patients by ethnic group (p = 0.029).In univariate analysis only South Asian (HR = 0.82, 95%CI; 0.67-1.00) showed slightly better survival comparingto Other. In multivariate analyses, South Asians showedbetter survival compared to the Other ethnicity group inthe individual group comparison, however the overalldifference among ethnic groups was not significant(Table 4). A significant survival difference only wasobserved among ethnic groups for patients with non-metastatic disease (p = 0.0498), as shown in Figure 5.Again, South Asians showed better survival compared tothe Other ethnicity group (HR = 0.74, 95%CI; 0.56-0.97)in the multivariate analysis.DiscussionAn earlier population-based study in BC reported over-all five-year survival rates of 8.8% for esophageal cancerand 16.2% for gastric cancer [21]. The current study wasconducted to examine the effect of ethnicity on survival.The selection of ethnic groups was based on the predo-minant ethnic groups in the BC population and avail-ability of ethnicity information. Our results indicate thatpatient ethnicity is a prognostic factor for both gastricand esophageal cancer; however ethnicity is onlyan independent prognostic factor for gastric cancerpatients.Ethnicity may represent biological characteristics ofpatients. Genetic variation may be responsible for differ-ences in tumor-host interactions, such as the micro-architecture of tumors [22] and the complex process ofmetastasis, both of which are influenced by host geneticpolymorphisms [23]. Ethnicity may also determine life-style and environmental characteristics including cul-tural, socioeconomic, and religious practices. Suchdifferences are expected to be less apparent withincreasing generations after immigration. Additionally,migration itself is one of the determinants of health out-come, and the “healthy migrant effect” could explainsome of the observed survival difference among ethnicgroups [24]. The difference in patient survival is notlikely to be due to healthcare disparities among minoritygroups, as all BC residents receive free healthcarethrough the BC Medical Services Plan (MSP). Interest-ingly, survival was found to be better in minority groupscompared to the BC general population.Prognostic factors can be classified into three broadgroups: i) tumor-related, ii) host-related, and iii) envir-onment-related (including healthcare, treatment andlifestyle) factors [25,26]. Among tumor-related prognos-tic factors, disease stage is the most important [26] andoften strongly influences the treatment plan. There wereno significant differences in the stage distributionsamong ethnic groups; however, survival differencesamong ethnic groups were only significant for non-metastatic (i.e., stage I-III) disease. After adjustment forother factors (such as stage), the prognostic effect ofethnicity was significant only for gastric cancer patients.Location of tumor (i.e., tumor topography) is a poten-tial determinant of cancer survival. Our observationFigure 4 Survival of esophageal cancer patients by ethnicgroup.Table 4 Effect size of ethnicity for overall survival ofesophageal cancer patientsEthnicity N HR 95% CI PIranian 10 1.13 0.61 2.12Chinese 95 0.9 0.72 1.13 0.14South Asian 81 0.8 0.59 0.98Other 1947 ReferenceHazard ratio (HR) and 95% confidence interval (CI) from Cox proportionalhazards regression analysis adjusted for patient sex, patient age, year ofdiagnosis, tumor histology, tumor location, tumor stage and treatment.Figure 5 Survival of esophageal cancer patients by ethnicgroup for non-metastatic disease.Bashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 6 of 8indicates significant differences in tumor location amongdifferent ethnic groups. It has been shown previously inWestern countries that gastric cardia tumors are asso-ciated with worse survival compared to distal gastrictumors [27-29]. In addition, for studies of esophageal can-cer, the location of tumors also showed differences in sur-vival. Tumors in the middle 1/3 of the esophagus showworse survival in Turkey and Ardabil (Iran) [30,31], buttumors in the lower 1/3 of the esophagus are reported tohave worse survival in BC and the United States[21,32].Among host-related prognostic factors, ethnic differ-ences were found for sex and age in both gastric andesophageal cancer. Of environment-related factors, treat-ment is likely the most powerful determinant of survival.There were significant ethnic differences in the propor-tions of gastric cancer patients who received surgeryand chemotherapy. The reason for treatment differencesamong ethnic groups is not clear in a system where allpatients have equal access to cancer care, but the differ-ences might be explained by disease factors, otherpatient characteristics or patient preferences.The result for gastric cancer is consistent with severalUS studies in which all other ethnic groups had bettersurvival compared to the non-Hispanic white population[33], and a Los Angeles study that showed that Asianswith gastric adenocarcinoma had superior outcomescompared to other ethnic groups [34]. Our study alsoconfirms the findings of an earlier study in BC thatreported better survival outcomes for gastric cancerpatients with Asian ethnicity compared to the generalpopulation [35]. Our findings are consistent with inter-national population-based cancer survival data that indi-cate that the 5-year survival for gastric cancer in Chinais higher than in India [36]. A comparison betweenregistries from Shanghai (China) and Madras (India)shows that the 5-year relative survival for gastric (20%versus 7.5%) and esophageal cancer (9.0% versus 6.9%)is better in Shanghai [37]. These survival rates for bothcancers are also higher than those reported in Iran [38].It has been suggested that lower quality care and dis-parities in treatment are major contributors to differ-ences in survival between minority and non-minoritypopulations [39]. BC residents have access to publicly-funded healthcare, and the BC Cancer Agency (BCCA)has developed province-wide treatment guidelines andprotocols [40].Strengths and limitationsThe main strength of this study is the availability of reli-able population-based data with details on tumor histol-ogy and pathology, treatment, disease stage and survivaloutcomes. The main limitation of this study is the lackof self-reported ethnicity information, requiring the useof a proxy method (i.e., name lists) to assign ethnicity.The weakness of using name lists as proxy for ethnicityis greater for women, who may change their surnamesafter marriage. Women account for only 30% of gastricand esophageal cancer cases in BC[21], but the possibi-lity of misclassification in this subset must be consid-ered. Based on a Statistics Canada report, visibleminorities in Canada are a relatively young group andonly 29% are older than 45 years, compared with 41% inthe general population that are older than 45 http://www40.statcan.ca/l01/cst01/demo50a-eng.htm. Gastricand esophageal cancer is diagnosed at a late age and theobserved survival differences between ethnicities in thisstudy might be due to age distributions.ConclusionsOur study investigated ethnicity as a prognostic factor forgastric and esophageal cancer patients. It has been shownthat for gastric cancer, patient ethnicity is significant andChinese patients experience better survival than peoplefrom the Other ethnicity (i.e., non-South-Asian, non-Chi-nese and non-Iranian) group. Despite the observed survi-val benefit for gastric cancer patients who are Iranian,the low number of patients in this ethnic group does notpermit a meaningful interpretation. Our results also indi-cate that, for esophageal cancer, South Asians have bettersurvival compared to the Other ethnicity group.Gastric and esophageal cancers are deadly diseasesthat are often diagnosed at a stage when the treatmentoptions are limited and less effective. Ethnicity mayrepresent underlying genetic factors. Such factors couldinfluence host-tumor interactions by altering tumoretiology and therefore its chance of spreading. Alterna-tively, genetic factors may determine response to treat-ments. Finally, ethnicity may represent non-geneticfactors that affect survival. Differences in survival byethnicity support the importance of ethnicity as a prog-nostic factor, and may provide clues for the future iden-tification of genetic or lifestyle factors that underliethese observations.List of abbreviationsBCCA: BC Cancer Agency; BCCR: BC Cancer Registry; CI: confidence interval;GI: gastrointestinal; HR: hazard ratio; ICD-O: International Classification ofDiseases for Oncology; MSP: BC Medical Services Plan; NES: not elsewherespecified; NOS: not otherwise specified; SMPBC: Screening MammographyProgram of British Columbia;Acknowledgements and FundingMB holds a Studentship funded by the Canadian Cancer Society (STU-08-019764). CB and AB-W are Senior Scholars of the Michael Smith Foundationfor Health Research.Author details1Cancer Control Research Program, BC Cancer Agency, Vancouver, Canada.2Interdisciplinary Oncology Program, University of British Columbia,Vancouver, Canada. 3Medical Oncology, BC Cancer Agency, Vancouver,Canada. 4Canada’s Michael Smith Genome Sciences Centre, BC CancerBashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 7 of 8Agency, Vancouver, Canada. 5Department of Medicine, University of BritishColumbia, Vancouver, Canada. 6School of Population and Public Health,University of British Columbia, Vancouver, Canada. 7Department of Statistics,University of British Columbia, Vancouver, Canada. 8Department ofBiomedical Physiology and Kinesiology, Simon Fraser University, Vancouver,Canada.Authors’ contributionsMB designed the study, performed the analysis and wrote 100% of themanuscript. AS supervised clinical aspects of the study and reviewed themanuscript. GH supervised epidemiological aspects of the study andreviewed the manuscript. NL supervised statistical aspects of study andreviewed the manuscript. CB and ABW supervised all aspects of study,contributed to the interpretation of findings, and reviewed the manuscript.Competing interestsThe authors declare that they have no competing interests.Received: 19 November 2010 Accepted: 9 May 2011Published: 9 May 2011References1. Parkin DM, Bray F, Ferlay J, Pisani P: Global Cancer Statistics, 2002. CA: ACancer Journal for Clinicians 2005, 55(2):74-108.2. Kamangar F, Dores GM, Anderson WF: Patterns of cancer incidence,mortality, and prevalence across five continents: defining priorities toreduce cancer disparities in different geographic regions of the world. JClin Oncol 2006, 24(14):2137-2150.3. Crew KD, Neugut AI: Epidemiology of gastric cancer. World J Gastroenterol2006, 12(3):354-362.4. Allen JW, Richardson JD, Edwards MJ: Squamous cell carcinoma of theesophagus: a review and update. 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[http://www.bccancer.bc.ca/HPI/CancerManagementGuidelines/default.htm].Pre-publication historyThe pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2407/11/164/prepubdoi:10.1186/1471-2407-11-164Cite this article as: Bashash et al.: The prognostic effect of ethnicity forgastric and esophageal cancer: the population-based experience inBritish Columbia, Canada. BMC Cancer 2011 11:164.Bashash et al. BMC Cancer 2011, 11:164http://www.biomedcentral.com/1471-2407/11/164Page 8 of 8


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