This study showed that the incidence rates of gastric cancer significantly differed according to age. Accordingly, our recommended screening intervals were based on age brackets. For patients over 70 years old, screening for gastric cancer every year may be appropriate, and for patients 60–69 years old, every two or three years, for patients 50–59 years old, every three or four years, and for patients 40–49 years old and under 40 years old, every five years.
In the group of participants older than 70 years old, approximately 0.5% developed gastric cancer within the next year. The proportion of the incidence of gastric cancer to the number of biopsies was 7 / 145 (4.8%) compared to 35 / 964 (3.6%) in all participants. Having adjusted for multiple variables using GEE model, the odds ratio for the incidences of gastric cancer within the next year turned to be 1.46 (95%CI: 1.06-2.02). Cancer screening tends to be controversial in elderly people because of their remaining life expectancy. However, in Japan, the life expectancy is 80 years old for males and 86 years old for females [24
], long enough for justifying cancer screening for people aged over 70 years.
For the 60–69 year-old age group, the incidence of gastric cancer exceeded 0.5% within the next three years. The proportion of the incidence of gastric cancer to the number of biopsies was 13 / 289 (4.5%), and the proportion was higher than for gastric cancer in all participants. In the GEE model, the odds ratio for the incidence of gastric cancer within the next year was 1.59 (95%CI: 1.23-2.06). Therefore, screening every two or three years may be appropriate.
For patients 50–59 years old, the incidence of gastric cancer was approximately 0.5% within the next four years. The proportion of the incidence of gastric cancer to the number of biopsies was 12 / 344 (3.5%), similar to the proportion of gastric cancer in all participants. Based on the GEE model, the odds ratio for the incidence of gastric cancer within the next year was 1.94 (95%CI: 1.31-2.86), and it was the highest among all the groups. Therefore, screening every four years may be reasonable.
For patients 40–49 years old, the incidence of gastric cancer was less than 0.5% within the next five years. The proportion of the incidence of gastric cancer to the number of biopsies was 3 / 159 (1.9%), and the proportion was lower than that for all participants. Based on the GEE model, the odds ratio for the incidence of gastric cancer in the next year was 1.51 (95%CI: 0.91-2.49), which attained no statistically significance. Therefore, screening every five or more years may be considered. However, in this group, all patients with gastric cancer had signet cell carcinoma, which has poor prognosis. This means that screening patients in this group may have to be considered carefully.
Among those under 40 years old, there were no patients with gastric cancer. Therefore, screening every five or more years may be appropriate for this age bracket.
In our study, 20 of 29 (69.0%, 95%CI: 49.2-84.7) patients with gastric cancer (excluding MALT lymphoma because of the differences in treatment) were detected in the early stage and treated with ESD. Compared to a previous study on barium x-ray screening program, the early stage detection rate in our study was high [25
]. It is speculated that early detection of gastric cancer by nation which screening program in Japan has contributed to the reduced mortality from gastric cancer in the past decades [7
]. In this regard, gastric cancer screening using EGD which detects gastric cancer in earlier stage than barium X-ray may be efficient.
In addition to that, early detection for gastric cancer was expected better prognosis than late detection. Previous study reported that the five years survival rate with gastric cancer in Stage I, II, III, IV were 99.1%, 72.6%, 45.9%, and 7.2% respectively in Japan [26
]. Among 24 patients with adenocarcinoma, at least 20 patients were in Stage IA or IB in our study. Within them, 16 patients were treated by ESD, which was less invasive than gastrectomy. Therefore, patients in our study were expected not only early detection for gastric cancer, but also better prognosis.
There are some limitations to this study. First, this study was a retrospective cohort study. We could not determine the magnitude of false negative results. There is a report, however, which reported that the false negative rate for gastric cancer screening by EGD was nil while 12 months follow-up [27
]. Therefore, we would think the effect of false negatives negligible in our study. Second, our data did not include information on H. pylori
. It is said that 70-80% of people over 40 years old in Japan had H. pylori [
]. A previous randomized controlled study showed that H. pylori
eradication reduced precancerous lesions without affecting overall incidence of gastric cancer [29
]. For this reason, the information on H. pylori
infection is unlikely to affect our results from 5 years cohort study. Third, population in our study may have selection bias, because of the study design. However, the incidence of gastric cancer in our study was similar to that in the previous study in Japan [30
]. Therefore, this is also unlikely to affect the result. Finally, our data didn’t have the information of atrophic gastritis. Previous study revealed that atrophic gastritis may be a major cause of gastric cancer [31
]. For these reasons, additional studies are required to further evaluation.