Anti-Helicobacter pylori antibodies prevalence and gastric adenocarcinoma in Portugal: report of a case-control study

Evidence from large cohort studies has established an increased risk of gastric cancer for individuals infected with Helicobacter pylori (HP). In low incidence countries, like the United Kingdom and Sweden, case-control studies suggested that the prevalence of anti-HP antibodies in gastric cancer patients (at the time of cancer diagnosis) is greater than in control populations. We present results from a case-control study of the prevalence of IgG anti-HP antibodies in gastric cancer patients and a control population in a country with a high incidence of gastric cancer. Sera were studied from 80 gastric cancer patients (GC group) admitted consecutively to our department in 1990/91, and from 80 controls (CT group) matched by age and sex. IgG anti-HP was determined by ELISA. Patients' files were reviewed for evidence of previous diagnosis of peptic ulcer, gastric surgery, tumour localization and histopathological classification. Controls were submitted to a questionnaire for past history of peptic ulcer and gastric surgery. Positive results for anti-HP were: gastric cancer patients, 70.0%; control group, 81.5% (NS). However, the median optical densities (OD, a measure of antibody concentration) were significantly lower in the gastric cancer group than in controls: gastric cancer patients, 0.720 ± 0.424 OD; control group, 0.906 ± 0.443 OD (P = 0.004). There were no differences concerning past history of peptic ulcer or surgery. The proportion of positives for cancer of the cardia (66.7%) was lower than for the other tumour localizations (70.4%) (NS). Anti-HP positivity was lower in patients with gastric cancer associated with intestinal metaplasia than in controls (P = 0.14). No difference in positivity was found between diffuse and intestinal type of gastric cancer. Our results suggest that, in contrast to results from low incidence countries, the prevalence of anti-HP antibodies in gastric cancer patients is not different from controls in this high incidence country. The reason for this may be the high prevalence of anti-HP antibodies in the general population. The lower optical densities in cancer patients may be due to older infections or the development of a hostile environment for HP (like intestinal metaplasia), with low levels of HP colonization in advanced stages of carcinogenesis.