We conducted a case‐control study to evaluate the effect of Helicobacter pylori (HP) infection on the risk of gastric cancer in Tokyo, Japan. The sera at the time of diagnosis from 282 gastric cancer cases and 767 sex‐ and age‐matched cancer‐free controls were tested for the presence of anti‐HP IgG antibody (HM‐CAP ELISA kit) and serum pepsinogen (PG) level (PG I and PG II Riabead). No significant association was observed in all sets [matched odds ratio (OR)=1.04, 95% confidence interval: 0.73–1.49]. In subgroup analyses, however, an association was suggested in females [OR=1.57], a younger population (<50 years) [OR=1.86], early cancer [OR=1.53] and small cancer (<40 mm) [OR=1.55]. Furthermore, we observed a tendency for odds ratios to decrease with an increase in age or cancer growth (depth of tumor invasion and tumor size). Considering that the spontaneous disappearance of HP due to extended mucosal atrophy may lead to these decreasing odds ratios, we applied the conditional logistic model adjusted for the PG I/II ratio as a measure of atrophic gastritis. This analysis showed a positive association with HP infection in all sets [OR=1.69; 1.01–2.81], distal cancer [OR=1.88; 1.07–3.31] and intestinal‐type cancer [OR=3.76; 1.39–10.18]. We concluded that the risk of cancer associated with HP infection may be underestimated in studies with cross‐sectional exposure because of spontaneous disappearance of HP due to extended mucosal atrophy.

The endoscopic appearances of the gastrointestinal lymphomas differ widely, and it is often difficult to make the distinction between a benign lymphoproliferative disorder and a malignant lymphoma even with a histologic evaluation. Since almost all primary malignant lymphomas of the gastrointestinal tract are of B‐cell origin, the confirmation of monoclonality in immunoglobulin (Ig) is helpful for differential diagnosis. Rearrangements of the Ig heavy chain gene were examined by polymerase chain reaction (PCR) analysis in frozen biopsy specimens of human stomach. The sensitivity of the analysis was sufficient to detect even a 5% clonal B‐cell proliferation and results could be obtained within 17 h. In a clinical investigation, seven of eight cases (88%) of primary gastric malignant lymphoma showed a single band in polyacrylamide gel electrophoresis (PAGE) after PCR, suggesting a monoclonal proliferation of B‐cell lineage. By contrast, all seven cases of reactive lymphoreticnlar hyperplasias showed a broad smear pattern in PAGE, which is thought to reflect polyclonal proliferation. None of the lymphocytes infiltrating around gastritis (7 cases), gastric ulcers (12 cases) and gastric carcinomas (15 cases) showed a monoclonal proliferation pattern. These findings suggest that detection of monoclonality in Ig heavy gene rearrangement by PCR is useful for the differential diagnosis of B‐cell lymphoproliferative diseases in the gastrointestinal tract.

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