Relation between goiter and autoimmune thyroid disease, and gastric cancer

In a Chinese cohort of 29,584 adults (participants to the Linxian General Population Nutrition Intervention Trial) followed from 1986 to 2001 and including 1,440 cases of gastric cancer, 1,949 of esophageal cancer and 425 subjects (59 among cases) who reported history of goiter, Abnet et al.1 found goiter associated with an increased risk of gastric noncardia adenocarcinoma. The hazard ratio (HR) was 2.04 (95% confidence interval, CI, 1.01–4.11). The HR were 1.45 (95% CI, 0.91–2.30) for gastric cardia adenocarcinoma and 1.37 (95% CI, 0.97–1.94) for esophageal squamous cell carcinoma. Iodine is concentrated by the gastric mucosa, where it may act as an antioxidant, thus, iodine deficiency, and hence goiter, may be associated with an increased risk of gastric cancer.2 Only a few studies investigated this issue. A study from Turkey3 reported that 49% of 61 gastric cancer cases versus 20% of 55 controls had history of goiter, and cases also reported more frequently thyroid autoimmune disease than controls. Another Turkish study of 19 cases found a lower iodine concentration in gastric cancer tissue than in surrounding normal tissue.4 An Iranian study5 showed that gastric cancer patients excreted more iodine than controls. To investigate the relation between thyroid diseases and gastric cancer risk in a developed country, we analyzed data from a hospital-based case-control study conducted between 1985 and 1997 in the Greater Milan area.6 Briefly, this included 769 incident, histologically confirmed cases of stomach cancer (469 men and 300 women; median age 61 years, range 19–79 years). The controls were 2,081 subjects (1,220 men, 861 women, median age 55 years, range 19–79 years) admitted to the same hospital network as cases for acute conditions other than neoplastic or digestive tract diseases and unrelated to long-term diet modification (46% traumas, 20% other orthopaedic conditions, 19% acute surgical, 15% other miscellaneous disorders). Less than 4% of identified cases and controls refused to be interviewed. Cases and controls were interviewed during their hospital stay using a standard questionnaire, including information on sociodemographic characteristics, anthropometric measures and information on smoking, alcohol, frequency of consumption of 29 food items and a problem-oriented medical history, including 16 diseases or conditions. Among these, there were thyroid diseases, which were subsequently classified as goiter, nodules/adenoma, hyperthyroidism and other or unidentified benign thyroid diseases. Odds ratios (OR) and the corresponding 95% CI were estimated using unconditional multiple logistic regression models, including terms for age, sex and education. Table I gives the distribution of cases and controls according to various thyroid conditions. The frequency of all of these ranged between 0.4% and 1.2%. No relation was found between history of various benign thyroid diseases and gastric cancer risk. The OR was 0.70 (95% CI, 0.19–2.65) for history of goiter, 0.61 (95% CI, 0.23–1.64) for thyroid nodules/adenomas, 1.10 (95% CI, 0.47–2.57) for hyperthyroidism, and 0.71 (95% CI, 0.32–1.57) for other or not specified benign thyroid diseases. In this study, we were not able to distinguish between various subsites of gastric cancer, but the incidence of gastric cardia cancers between 1985 and 1992 in Italy was only around 10% of total gastric cancers.7 Thus, our results refer mainly to noncardia gastric cancers. Among the advantages of the study, there is the relatively large dataset, the practically complete participation of cases and controls approached, and the reliability of information on medical history (r = 0.85 for thyroid conditions8). The study power, however, is limited by the small proportion of cases and controls with history of goiter and thyroid conditions. At the time of study conduction, gastric cancer was common in Italy, and was still the third cause of cancer death after lung and colorectal cancer.9 Furthermore iodized salt is not routinely used by the Italian population and mild iodine deficiency is not rare in the country.10 Still, goiter and other thyroid diseases do not appear to be a relevant cause of gastric cancer in Italy. Yours sincerely, The authors thank Ms. I Garimoldi for editorial assistance. Marta Rossi, Eva Negri, Roberto Foschi, Silvia Franceschi, Carlo La Vecchia.