Time trends for small gastric cancer in Japan

BACKGROUND: Gastric cancer rates in Japan have been declining since the 1970s. The rate of differentiated carcinomas has decreased and that of undifferentiated carcinomas has increased. However, little is known about the time trends of small gastric cancer. The aim of this study was to investigate the trends of small gastric cancer over time in Japan. METHODS: We reviewed cases of small gastric cancer (less than 20 mm in diameter) in two groups of patients who entered the age range of 55-to-67 years 14 years apart: patients in cohort 1 (n = 66) were born between 1899 and 1912, and those in cohort 2 (n = 66) were born between 1926 and 1936. Between-group comparisons were made for macroscopic, microscopic, and histochemical findings. Mucin histochemical analysis was used to investigate gastric and nongastric phenotypes. Helicobacter pylori was also investigated by immunohistochemistry. RESULTS: There were significant decreases in the incidence of elevated carcinoma (20% in cohort 1 vs 6% in cohort 2; P < 0.05) and papillary adenocarcinoma (11% vs 2%; P < 0.05). The incidence of flat carcinomas was significantly increased (3% vs 15%; P < 0.05). The incidence of tumors surrounded by fundic gland mucosa increased (20% vs 29%), whereas that of tumors surrounded by intestinal metaplastic mucosa decreased (52% vs 41%). The rate of H. pylori infection in mucosa surrounding tumors was the same in both groups (35%). The incidence of tubular adenocarcinoma with gastric-type mucin was higher in cohort 2 (64%) than in cohort 1 (51%). CONCLUSION: The rate of tubular adenocarcinomas containing gastric type mucin has increased over time. These tumors had a tendency to develop in the fundic gland mucosa and to show less intestinal metaplasia. The H. pylori infection rate was unrelated to this time trend. In advanced gastric cancer, the differentiated carcinoma rate has decreased; however, in small gastric cancer, the rate of tubular adenocarcinoma containing gastric type mucin has increased. This suggests that tubular adenocarcinoma with gastric type mucin changes into poorly differentiated adenocarcinoma as tumors grow to advanced stages.