Epidemiologic trends and geographic distribution of esophageal cancer in Canada: A national population‐based study

Abstract Background Esophageal cancer can be subdivided into two main histological subtypes with significant variability in their etiology and epidemiology. The incidence of esophageal adenocarcinoma (AC) is increasing across the developed countries, whereas the incidence of esophageal squamous cell carcinoma (SCC) is declining. Several risk factors have been identified in the pathogenesis of each subtype, however, their epidemiologic characteristics and distribution throughout Canada remain poorly understood. Methods We performed a retrospective analysis of demographic data across Canada from 1992 to 2010 using two independent population‐based cancer registries. The incidence of esophageal cancer, for each subtype, was examined at the levels of provinces/territories, cities, and postal codes. Results A total of 19 790 patients were diagnosed with esophageal cancer in Canada between 1992 and 2010; 74% were males. The average national incidence rate was 33.5 cases per million individuals per year. Incidence of esophageal AC increased over time, with notable high‐incidence rates on the Vancouver Island, the coasts of the Great Lakes, and the coasts of the Northumberland Strait in the Maritimes. The overall incidence of esophageal SCC has decreased. However, high incidence of esophageal SCC was detected in the Vancouver city, rural eastern Québec, and in the Maritimes. We also report clustering for each subtype using postal codes, which sheds light onto new avenues of research for potential environmental etiologies. Conclusions This study, for the first time, provides a detailed analysis on the burden of esophageal cancer in Canada, revealing important geographic clustering trends.

databases employed, the data must be vetted in order to verify compliance with the variety of confidentiality regulations. SSHRC/Statistics Canada requires that each cell count be rounded to a multiple of 5 using a random rounding system. In addition, no counts 1 and 5 of cases can be released. Therefore, we were able to delineate high incidence communities, as well as locate areas in the country, where zero cases were documented between 1992 and 2010, designated as low incidence areas.
Incidence rates and 95% confidence intervals (CI) were calculated and reported overall, by year of diagnosis and specific geographic regions that were identified by the mapping analysis.
CIs were based on exact Poisson tests. Statistical significance was defined by 95% CI not overlapping with that of the national average 95% CI. The national age-standardized incidence rates for esophageal cancer and its subtypes were calculating using the WHO population standard 1 .
The age-standardized incidence rates by province and by FSA for esophageal cancer and its subtypes were calculated using the Canadian population standard between 1992 and 2010.
Incidence rates were plotted, and linear regression models were used to assess trends over time.
Geographic maps of Canada, indicating the place of residence of patients recorded by the CCR and LRQC databases, were generated using geographic information systems software (Tableau 10.3 from Tableau Software, Seattle Washington, USA). Only FSAs with populations of at least 5,000 individuals based on census data were selected in order to reduce the risk of false-positive hits which could inflate the incidence rate.

Analysis of esophageal adenocarcinoma
Of the 53 cities with high incidence of esophageal AC in Canada (Supporting Table 3A), 15 (28%) were found in BC, 6 (11%) in NS, 2 (0.04%) in NB and 1 (0.02%) in PEI. Most importantly, 26 (49%) of these high incidence cities were located in Ontario. On closer inspection of these cities, 20 (77%) were located on the coasts of the four Great Lakes: Superior, Huron, Eerie and Ontario. On the other hand, of the 37 low-incidence cities in Canada (Supporting Table 3B), 20 (54%) were located in Quebec, which also had a significantly lower provincial incidence than the national average.

Analysis of esophageal squamous cell carcinoma
Of the 21 cities with the highest incidence of esophageal SCC in Canada (Supporting Table 5A), 8 (38%) were found in ON, 6 (29%) in BC, three (14%) in QC, two (9%) in SK, and one (5%) each in AB and MB. In contrast, of the 59 low-incidence cities (Supporting Table 5B), 27 (46%) were located in ON, 24 (41%) were located in QC, 3 (5%) in AB, 2 (3%) each in BC and NS, and finally 1 (2%) in NL. Four other FSAs were located nearby in various parts of Vancouver (V7V, V5M) and Burnaby (V5C, V5H). Several additional FSAs were noted on British Columbia's west coast, particularly on the Central Vancouver Island (V0P), Campbell River (V9W), and Parksville (V9P). Finally, the region of Saanich was significantly affected with a cluster in Sidney (V8L), and Victoria (V8X and V8R), seen in Figure 5A. Several rural regions of Québec displayed a higher incidence than the national average, namely in Gaspésie (G0E) and Bas-Saint-Laurent-Est (G0K) which border Saint-Basile (E7C), a high incidence FSA in NB ( Figure 5B). In NS (Figure 5C), the north-eastern territory and Cape Breton had higher incidence, with North Victoria County (B0C), Antigonish (B2G), Sydney (B1P, B1V) having significantly higher incidence than the national average. In NL (Figure 5D), significant high-incidence FSAs were found in St. John's (A1C) and on the Western Avalon Peninsula (A0B). Low incidence of esophageal SCC was identified in 21 areas (Supporting Table 6). Eight FSAs each were found in QC and ON, corresponding to 38% each of low incidence regions in Canada. Three quarters (6/8) of the ON cities were located in the GTA, and all eight of the areas in QC were found in the Greater Montreal Area.

Reference:
Supporting Table 1A-B: Crude incidence of esophageal cancer in Canadian cities. Cities are divided into high incidence, and low incidence compared to the average esophageal cancer incidence rate in Canada. All case numbers are rounded to the nearest 5. All population numbers are rounded to the nearest ten.

A0A
NF 0 Table 3A-B: Crude incidence of esophageal adenocarcinoma in Canadian cities. Cities are divided into high incidence, and low incidence compared to the average esophageal adenocarcinoma incidence rate in Canada. All case numbers are rounded to the nearest 5. All population numbers are rounded to the nearest thousand. Cities are divided into high incidence, and low incidence compared to the average esophageal squamous cell carcinoma incidence rate in Canada. All case numbers are rounded to the nearest 5. All population numbers are rounded to the nearest ten.