Introduction

Double-contrast upper gastrointestinal barium X-ray radiography (UGI-XR) is the most widely used method for gastric cancer screening in Japan [1]. Since the 1960s, the UGI-XR-based gastric cancer screening program endorsed by the Japanese government has achieved a significant reduction in mortality and morbidity of gastric cancer [1–3]. UGI-XR can detect not only gastric cancer but also gastroduodenal erosion or ulcer, gastric or esophageal polyps, esophagogastric diverticula, atrophic or hypertrophic gastritis, esophageal hiatal hernia, and other lesions [4, 5]. Of these various lesions, gastric polyp is one of the most frequent findings observed in the usual screening examination [6]. Nowadays, however, it is a matter of controversy how to manage the gastric polyps detected by UGI-XR. Actually, the clinical steps after detecting gastric polyps by UGI-XR are quite varied in Japan. Some UGI-XR examinees diagnosed with gastric polyps are recommended to undergo a detailed examination with upper gastrointestinal endoscopy (UGI-ES), whereas other examinees are advised to obtain a follow-up survey because the risk of developing gastric cancer is low. “Gastric polyp” is a mere morphological entity including protruded gastric mucosa of various histology [7–10], and the distribution of its histological types shows marked regional differences around the world [6, 11–13].

Recently, two international guidelines of gastric polyps were released from the United States (US) and UK [7, 9]. The former is a pathology-based guideline targeting both epithelial and nonepithelial lesions [9], which is mostly based on a large-scale nationwide survey in the US [8]. In contrast, the latter mostly focuses on epithelial lesions using the GRADE (grading of recommendations, assessment, development, and evaluation) system to develop a guideline consensus [7]. Regardless of the several differences, both guidelines recommend forceps biopsy for histological evaluation of gastric polyps. Performing biopsy is not difficult under UGI-ES, which can histologically evaluate such types of gastric polyps as fundic gland polyps, hyperplastic polyps, adenomatous/cancerous polyps, inflammatory fibroid polyps, and hamartomatous polyps [7–10]. Conversely, however, it is impossible to execute a biopsy in the procedure of UGI-XR: the aforementioned guidelines are not easily applied for UGI-XR-detected gastric polyps.

Based on this background, the risk of future gastric tumorigenesis should be evaluated to determine what to do when gastric polyps are detected by UGI-XR. Several risk factors, such as chronic H. pylori infection [14, 15], male gender [16, 17], salt intake [18, 19], and smoking [20–23], adversely affect gastric tumorigenesis. It is now established that H. pylori infection is by far the strongest risk factor among them [14], and it is also established that H. pylori-induced “mucosal atrophy” (atrophic gastritis) and “enlarged gastric folds” (hypertrophic gastritis) are both obvious predictive indicators for future gastric cancer incidence [24, 25]. During this half century, the prevalence of H. pylori infection has considerably decreased not only in Japan but also worldwide [26–29]. Accordingly, the prevalence of various H. pylori-related gastric polyps must have changed, but recent epidemiological data concerning gastric polyps are insufficient.

In the present study, using the large-scale data of generally healthy subjects in Japan, we analyzed the characteristics of UGI-XR/UGI-ES-detected gastric polyps. We believe the present results can reflect the background factors and histological breakdown of gastric polyps in East Asia today. We are also convinced that our data will be useful for the strategy against gastric polyps not only those detected by UGI-XR but also those found by other medical examinations.

Methods

Study subjects

The study participants were 20,773 asymptomatic generally healthy subjects who underwent a medical checkup in 2010 at our institute (Chiba-shi, Chiba, Japan). After excluding 892 subjects with insufficient data, 215 subjects with a history of gastrectomy, 1,517 subjects with past eradication of H. pylori, and 885 subjects using gastric acid suppressants (proton pump inhibitors or histamine H2-receptor antagonists), 17,264 eligible subjects were analyzed (Fig. 1). The total numbers of study subjects comprised 6,433 UGI-XR examinees and 10,831 UGI-ES examinees.

Fig. 1
figure 1

Study recruitment flowchart

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Follow-up strategy

All the study subjects were recommended to undergo an annual health checkup including gastric cancer screening. Data of UGI-XR and UGI-ES from the study participants were thoroughly obtained from 2010 to 2013. Although gastric cancer could be detected by UGI-XR or UGI-ES, the final diagnosis was confirmed by histopathology using the biopsy specimens.

Diagnosis of gastric polyps and atrophic gastritis by upper gastrointestinal X-ray (UGI-XR) examination

A method for UGI-XR was described in detail in our previous report [5]. Gastric polyps were diagnosed independently by two medical doctors specialized in gastroenterology or radiology and one radiologic technologist specialized in double-contrast X-ray imaging. Synthetic diagnoses from the judgments of these three specialists were used for the analyses. UGI-XR-based atrophic gastritis was classified into four types according to our recent reports as follows [5, 25, 30]: no atrophic gastric mucosa (type A), mild atrophic gastritis (type B), moderate atrophic gastritis (type C), and severe atrophic gastritis (type D).

Statistical methods

Univariate analysis was performed with the presence of gastric polyp as a response variable and seven background factors (age, gender, serum anti-H. pylori antibody, ratio of serum pepsinogen I/II, BMI, smoking, and drinking) as explanatory variables. Simple logistic regression was used for univariate analyses in which p < 0.05 was considered as statistically significant. Next, all the values were standardized, and the multiple logistic regression model was applied to calculate the standardized coefficients and odds ratios for the seven factors. A two-sided p value of less than 0.05 was considered statistically significant. To evaluate the association of the UGI-XR-detected gastric polyp with the four grade types of UGI-XR-based atrophic gastritis, the Cochran–Armitage test for trend was applied. A Kaplan–Meier curve was generated to assess the incidence of gastric cancer using JMP 10 software (SAS Institute), in which p < 0.05 was considered as statistically significant according to the log-rank test. All statistical analyses were performed using SAS version 8.2 (SAS Institute, Cary, NC, USA).

Results

Positively associated factors for the UGI-XR-detected gastric polyps based on univariate and multivariate analyses

The characteristics of the 6433 UGI-XR examinees focusing on the presence of gastric polyps are shown in Table 1. The univariate analyses revealed that age, gender, serum anti-H. pylori IgG, pepsinogen I/II ratio, BMI, and smoking status have significant association with the presence of gastric polyps. Our results indicated that the subjects diagnosed with gastric polyps by UGI-XR tend to be younger female subjects free from H. pylori infection and smoking habit, within the normal range of BMI, and having higher pepsinogen I/II ratio.

Table 1 Characteristics of the 6433 subjects, focusing on the presence of gastric polyps diagnosed by upper gastrointestinal barium X-ray radiography (UGI-XR)
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The following multivariate analysis showed that positively associated factors for the presence of UGI-XR-based gastric polyps in order of significance are lower value of serum anti-H. pylori IgG, female gender, lighter smoking habit, older age, and normal range of BMI (Table 2). Judging from the values of standardized coefficients, non-infection with H. pylori denoted the strongest positive association with gastric polyps by far. Female gender and lighter smoking habit showed the second and third strongest associations with polyps.

Table 2 Association between the presence of UGI-XR-detected gastric polyps and the seven factors based on the multivariate analysis
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UGI-XR-detected gastric polyps currently predominantly develop on the gastric mucosa with no atrophic change in Japan

In our recent reports, we demonstrated that UGI-XR can detect atrophic gastritis accurately [5, 30]: UGI-XR-based atrophy shows a strong and significant association with UGI-ES-based atrophy according to the Kimura–Takemoto classification [31]. In the present study, we analyzed the association between the four grade categories of UGI-XR-based atrophic gastritis [5, 30] and the presence of gastric polyps (Table 3). In Japan today, UGI-XR-detected gastric polyps predominantly develop on the gastric mucosa with no atrophic change (p < 0.0001), which is consistent with Table 2 revealing the significant positive association between the UGI-XR-detected gastric polyps and no infection with H. pylori.

Table 3 Association between the presence of gastric polyps and the four grade categories of atrophic gastritis diagnosed by UGI-XR (upper gastrointestinal barium X-ray radiography)
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The presence of gastric polyps suggests the present low risk of future gastric cancer development in Japan

At the end of the 3-year follow-up, 4919 subjects underwent UGI-XR or UGI-ES once or more often for gastric cancer screening. During this period, 7 subjects developed gastric cancer, but none of them had gastric polyps at the beginning of this study (Fig. 2a). Namely, our data indicate that all the gastric polyps detected by UGI-XR have not developed into gastric cancer for at least 3 years after the screening. The Kaplan–Meier curves evaluating the future incidence of gastric cancer could not detect a significant difference between the subjects with or without gastric polyps (Fig. 2b), but our data plainly suggest that future canceration of UGI-XR-based gastric polyps rarely occurs in Japan at present.

Fig. 2
figure 2

a Association between the presence of upper gastrointestinal barium X-ray radiography (UGI-XR)-detected gastric polyps and the development of gastric cancer in the 3-year follow-up of 6433 study subjects. b Kaplan–Meier curves to assess the 3-year incidences of gastric cancer focusing on the presence of gastric polyps, in which a p value less than 0.05 was considered as statistically significant according to the log-rank test

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Characteristics of the gastric polyps detected by upper gastrointestinal endoscopy (UGI-ES)

Because it is impossible to differentially diagnose the type of gastric polyps by UGI-XR, we analyzed the study participants who underwent UGI-ES in the same period (Fig. 1). Of the 10,831 UGI-ES examinees, 2,446 (22.6 %) had fundic (gland) polyps, 267 (2.5 %) had hyperplastic polyps, 9 (0.08 %) had adenomatous/cancerous polyps, and 8,112 (74.9 %) had no gastric polyps (Table 4). The rates of fundic, hyperplastic, and adenomatous/cancerous polyps among the 2,722 subjects with gastric polyps were 89.9 % (2,446), 9.8 % (267), and 0.3 % (9), respectively: these indicate that most of the gastric polyps detected nowadays in Japan are fundic gland polyps with no risk of future tumorigenesis. Distribution of the types of gastric polyps in the present study is in accordance with the recent reports not only from East Asia [6] but also from the United States [8].

Table 4 Characteristics of the 10,831 UGI-ES (upper gastrointestinal endoscopy) examinees classified into four groups based on the presence and types of gastric polyps
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Detailed characteristics of the subjects focusing on the UGI-ES-based gastric polyps are shown in Table 4. Fundic polyps with no risk of future canceration mostly developed on the H. pylori-negative gastric mucosa (96.8 %; 2368 of 2446). Conversely, hyperplastic polyps with some risk of future canceration tended to develop in the subjects with H. pylori infection (80.1 %; 214 of 267). Adenomatous/cancerous polyps with much higher risk of future canceration also predominantly developed in the H. pylori-positive subjects (88.9 %; 8 of 9).

Of the 10,831 UGI-ES examinees, gastric cancer lesions were detected in 12 subjects (0.11 %), which included 3 erosive, 2 ulcerative, 1 flat and protruded, and 6 depressed tumors (Table 4). The flat and protruded lesion (0–IIb and 0–IIa macroscopic type of early gastric cancer) may resemble benign gastric polyps to some extent, but the other 11 malignant lesions could not be mistaken for gastric polyps. Altogether, our results indicate that it is quite rare that the protruded type of early gastric cancer is wrongly diagnosed with a nonmalignant gastric polyp by UGI-XR.

Discussion

Our present results (Tables 1, 2, 3) clearly show that UGI-XR-detected gastric polyps in Japan today mostly arise from H. pylori-negative and non-atrophic mucosa with low risk of gastric cancer [14, 15]. In addition, prospective observation of the present cohort (Fig. 2) and evaluation of endoscopically diagnosed gastric polyps (Table 4) suggest that future canceration of UGI-XR-detected gastric polyps rarely occurs. As described in the "Introduction", clinical steps after detecting gastric polyps by UGI-XR are still controversial in Japan. Our results indicate that it is not efficient to perform UGI-ES for all the UGI-XR-detected gastric polyps. The greatest risk of follow-up observation without UGI-ES is to erroneously diagnose protruded early gastric cancers as nonmalignant gastric polyps, but our results indicate such misdiagnoses are quite rare.

Nowadays, it has been gradually accepted that UGI-XR can detect not only gastric cancer but also premalignant atrophic/hypertrophic gastritis [4, 25, 30, 32]. Our recent report demonstrated that UGI-XR can diagnose chronic H. pylori infection with very high accuracy (97.8 %; 1638 of 1674 subjects) [5]. Based on this accumulated evidence, we think that UGI-XR-detected gastric polyps should be evaluated together with UGI-XR-based atrophic or hypertrophic gastritis. Additional assessment of UGI-XR-based mucosal atrophy and enlarged gastric folds should help in predicting future risk of gastric cancer, because gastric polyps with malignant potential predominantly occur on H. pylori-positive gastric mucosa (Table 4). Although further data accumulation based on a longer observation period is needed, we at present conceive the follow-up observation without UGI-ES is an optimal strategy for UGI-XR-detected gastric polyps on the non-atrophic gastric mucosa. In contrast, we still recommend that UGI-XR-detected gastric polyps accompanied with atrophic or hypertrophic gastritis should be evaluated by UGI-ES as the second detailed examination.

Conclusions

A large-scale study of healthy people in Japan revealed that gastric polyps diagnosed by double-contrast barium X-ray radiography (UGI-XR) mostly arise on the Helicobacter pylori-negative gastric mucosa with a low risk of gastric cancer. In the prospective observation, none of the UGI-XR examinees with gastric polyps developed gastric cancer for at least the ensuing 3 years.