Abstract
Background: Stomach cancer is the fourth most common cancer in the world, but the second most frequent cause of cancer deaths. In Oman, stomach cancer is the most common cancer among males and existing data suggest that the age-standardised incidence rate of stomach cancer in Oman for both sexes is higher than the rates in many neighbouring Arab and Gulf Cooperation Council (GCC) countries. Possible reasons for this have not been explored. Population-based cancer research has only recently become possible in Oman, with the introduction of mandatory cancer registration and the establishment of a national death registration system (The Directorate General of Civil Status, DGCS).
Aims: The main aims of the research described in this thesis were:
- To describe the incidence of stomach cancer in Oman and to compare it to the incidence in surrounding GCC countries.
- To compare the prevalences of known risk factors for stomach cancer in Oman and other GCC countries.
- To provide population-based estimates of mortality, and median and relative survival of stomach cancer patients in Oman.
- To assess the feasibility of routinely undertaking linkage between the NCR and DGCS to monitor cancer survival.
Methods: Incidence data in Oman and the GCC countries were obtained from NCR and the Gulf Centre for Cancer Registration reports. The health literature and key websites were searched for information about the prevalence of risk factors in the GCC countries. To identify deaths, NCR records were linked with the DGCS and a parallel mortality database (PMD).
Results: The incidence of stomach cancer in Oman differed by sex, age and region, and showed a decline over time. The age-standardised incidence rate in Oman was higher than in most of the GCC countries, with some variation by age and sex. However, bias from incomplete registration was possible.
Smoking, BMI and fruit and vegetable intake were unlikely to explain the apparent between-country differences in stomach cancer incidence, but the lower socioeconomic status in Oman might contribute. Information regarding the prevalence of H. pylori infection and salt intake was lacking.
Because a unique identifier was missing from most NCR records, name, sex, address, and year of birth were used to search for death records in the DGCS and PMD. Matches were classified either as definite or possible. For definite matches, the median survival for males and females combined was 30 months (95% CI 16.3–.) and the one- and three-year relative survival rates were 0.70 (95% CI 0.62–0.78) and 0.58 (95% CI 0.49–0.67) respectively. When possible matches were included, the corresponding results were 14.7 months (95% CI 9.9–23.9), 0.60 (95% CI 0.52–0.68) and 0.44 (95% CI 0.36–0.53). There was evidence of incomplete death registration in both the DGCS and PMD. Mortality rates could not be estimated because of missing cause-of-death data.
Conclusions: The unavailability of comparable data on the prevalence of risk factors hinders the ability to identify possible reasons for the apparently higher risk of stomach cancer in Oman. Survival of stomach cancer patients in Oman seems to be poor. To better characterise the problem, the NCR and DGCS should continue improving the quality and completeness of their data, and ongoing monitoring of the burden of the disease seems desirable.