Soybean products intake has been suggested to have protective effects against breast cancer. As for lung cancer, we previously reported that soy consumption showed inverse association with the risk of non‐small cell lung cancers (NSCLC) with epidermal growth factor receptor mutations among Japanese. However, other possible heterogeneity of its effect on the etiology of NSCLC by background characteristics is still unclear. In this study, we investigated the impact of soy consumption on the development of NSCLC among larger number of Japanese women, with the association of smoking status, reproductive factors, as well as histology.

We conducted a case‐control study with 420 NSCLC women cases and 840 age‐sex matched control subjects. Dietary exposures were evaluated based on a semi‐quantitative food frequency questionnaire, including items on lifestyles, menstrual and reproductive history. Soy consumption was categorized into two groups: a lower third group, “Low consumption group (LCG)” which intake of soy was less than 30.3 mg/day, and others, “High consumption group (HCG)” which intake of soy were 30.3mg/day or more. We assessed the impact of soy consumption on lung cancer by calculating odds ratios (ORs) and their 95% confidence intervals (CIs) of HCG, relative to LCG with adjustment for potential confounding factors using logistic regression model.

In the overall analysis, we observed inverse association with high consumption of soy products [OR: 0.87, 95%CI: 0.65–1.16]. When stratified by smoking status, HCG in never smokers showed significantly inverse association showed an OR below unity [OR: 0.69, 95%CI: 0.50–0.96] in spite of the increased OR among HCG in ever smokers [OR: 2.02, 95%CI: 1.11–3.68]. As for reproductive factors, ORs of HCG were consistently below unity among women with pre‐menopause [OR: 0.55, 95%CI: 0.29–1.04], menopause after 50 years old [OR: 0.57, 95%CI: 0.34–0.94], and no delivery [OR: 0.57, 95%CI: 0.15–1.06]. It is interesting to note that on histology based analysis, we found inverse association between high consumption of soy products and adenocarcinoma [OR: 0.57, 95%CI: 0.34–0.94] among never smokers, despite the increased ORs were seen among ever smokers [OR: 3.35, 95%CI: 0.17–67.7].

In this study, consumption of soybean products generally demonstrated an inverse association with NSCLC. In addition, the results indicated the interaction between soy consumption and smoking status for the impact on the development of NSCLC. We also found associations among soy consumption, reproductive factors and lung cancer, which indicated that female hormonal factors might be involved in the etiology of NSCLC. Further epidemiological evaluation is warranted.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):B107.