Soy consumption reduces the risk of non-small-cell lung cancers with epidermal growth factor receptor mutations among Japanese

Soy Product Consumption and the Risk of Cancer: A Systematic Review and Meta-Analysis of Observational Studies

BACKGROUND

The association between soy product consumption and cancer risk varies among studies. Therefore, this comprehensive meta-analysis of observational studies examines the association between soy product consumption and total cancer risk.

METHODS

This study was conducted following the PRISMA guidelines. Up to October 2023, all eligible published studies were searched through PubMed and Web of Science databases.

RESULTS

A total of 52 studies on soy product consumption were included in this meta-analysis (17 cohort studies and 35 case-control studies). High consumption of total soy products (RR: 0.69; 95% CI: 0.60, 0.80), tofu (RR: 0.78; 95% CI: 0.70, 0.86), and soymilk (RR: 0.75; 95% CI: 0.60, 0.93) were associated with reduced total cancer risk. No association was found between high consumption of fermented soy products (RR: 1.18; 95% CI: 0.95, 1.47), non-fermented soy products (RR: 0.95; 95% CI: 0.77, 1.18), soy paste (RR: 1.00; 95% CI: 0.88, 1.14), miso soup (RR: 0.99; 95% CI: 0.87, 1.12), or natto (RR: 0.96; 95% CI: 0.82, 1.11) and cancer risk. A 54 g per day increment of total soy products reduced cancer risk by 11%, a 61 g per day increment of tofu reduced cancer risk by 12%, and a 23 g per day increment of soymilk reduced cancer risk by 28%, while none of the other soy products were associated with cancer risk.

CONCLUSION

Our findings suggest that high total soy product consumption, especially soymilk and tofu, is associated with lower cancer risk. More prospective cohort studies are still needed to confirm the causal relationship between soy product consumption and cancer risk.

Dietary factors and the risk of lung cancer by epidermal growth factor receptor mutation status and histological subtypes

Background

Previous studies have reported differential associations of certain dietary factors such as soy consumption by epidermal growth factor receptor mutant (EGFR +) subtype of non-small cell lung cancer (NSCLC). However, whether the other dietary factors including meat, fruits, and vegetables have differential risks on different histological and molecular subtypes of lung cancer remains unclear. Therefore, we conducted a case-control study to evaluate these associations.

Methods

A total of 3,170 cases and 4,238 controls from three different studies (Genes and Environment in Lung Cancer Study, Lung Cancer Consortium Singapore Study, and Multi-ethnic Cohort Study) were included. Information on demographics, lifestyle, and dietary consumption was obtained using questionnaires. Diet was assessed by using the number of standard servings of each item consumed per week. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between meat, vegetables, and fruits consumption with lung cancer risk after adjusting for potential confounders.

Results

We identified a significant inverse association between higher consumption of fruits and the risk of lung cancer (2nd tertile: OR = 0.54, 95%CI = 0.46-0.65; 3rd tertile: OR = 0.77, 95%CI = 0.65-0.91), compared with the lower (1st tertile) consumption of fruits. Higher vegetable consumption was significantly associated with a lower risk of EGFR + lung cancer (OR = 0.69, 95% CI = 0.54-0.88), however, this association was not significant among EGFR wild-type (-) lung cancer. Conversely, higher consumption of total meat (OR = 2.10, 95%CI = 1.58-2.79) was significantly associated with higher lung cancer risk, as compared with the lower consumption group.

Conclusions

Differential associations between vegetable consumption with EGFR mutation status in NSCLC were found. Further prospective studies are warranted to assess this association and elucidate the biological mechanisms.

Dietary phytoestrogen intake and lung cancer risk: an analysis of the Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial

Phytoestrogens (PEs) have estrogen-like activity and were found to lower incidences of several hormone-dependent cancers. Emerging evidence suggests that estrogen may play a role in lung cancer carcinogenesis. We aim to evaluate dietary PE intake and lung cancer risk using data from the Prostate, Lung, Colorectal, and Ovarian cancer screening trial. A total of 1,706 lung cancer cases were identified. The association between lung cancer risk and PE intake (in quartiles) was calculated using the Cox proportional hazard models adjusting for potential confounders. Stratified analyses by smoking status, sex, and histology were also performed. The highest quartile of total PE intake was associated with a reduced risk of lung cancer compared to the lowest quartile (HR=0.85, 95%CI: 0.73-0.99 for > 1,030 μg/day vs < 290 μg/day) (P trend=0.56). Similar patterns were observed among ever smokers (HR=0.84, 95%CI: 0.71-0.98), non-small cell histology (HR=0.84, 95CI: 0.72-0.99), male (HR=0.84, 95%CI: 0.69-1.03) and female (HR=0.80, 95%CI: 0.64-0.99 for 510-1,030 μg/day, HR=0.84, 95%CI: 0.67-1.06 for > 1,030 μg/day vs < 290 μg/day) subjects with no significant linear trend observed. Despite a lower consumption compared to the Asian population, increased PE intake still appears to decrease lung cancer risk in a Caucasian-dominant population. Future studies are needed to replicate these results in independent cohorts and shed a light on the potential mechanism of the protective effect of PEs on lung carcinogenesis and the interaction between PEs, smoking, and endogenous estrogens.

Vegetable intake and the risk of bladder cancer in the BLadder Cancer Epidemiology and Nutritional Determinants (BLEND) international study

BACKGROUND

Although a potential inverse association between vegetable intake and bladder cancer risk has been reported, epidemiological evidence is inconsistent. This research aimed to elucidate the association between vegetable intake and bladder cancer risk by conducting a pooled analysis of data from prospective cohort studies.

METHODS

Vegetable intake in relation to bladder cancer risk was examined by pooling individual-level data from 13 cohort studies, comprising 3203 cases among a total of 555,685 participants. Pooled multivariate hazard ratios (HRs), with corresponding 95% confidence intervals (CIs), were estimated using Cox proportional hazards regression models stratified by cohort for intakes of total vegetable, vegetable subtypes (i.e. non-starchy, starchy, green leafy and cruciferous vegetables) and individual vegetable types. In addition, a diet diversity score was used to assess the association of the varied types of vegetable intake on bladder cancer risk.

RESULTS

The association between vegetable intake and bladder cancer risk differed by sex (P-interaction = 0.011) and smoking status (P-interaction = 0.038); therefore, analyses were stratified by sex and smoking status. With adjustment of age, sex, smoking, energy intake, ethnicity and other potential dietary factors, we found that higher intake of total and non-starchy vegetables were inversely associated with the risk of bladder cancer among women (comparing the highest with lowest intake tertile: HR = 0.79, 95% CI = 0.64-0.98, P = 0.037 for trend, HR per 1 SD increment = 0.89, 95% CI = 0.81-0.99; HR = 0.78, 95% CI = 0.63-0.97, P = 0.034 for trend, HR per 1 SD increment = 0.88, 95% CI = 0.79-0.98, respectively). However, no evidence of association was observed among men, and the intake of vegetable was not found to be associated with bladder cancer when stratified by smoking status. Moreover, we found no evidence of association for diet diversity with bladder cancer risk.

CONCLUSION

Higher intakes of total and non-starchy vegetable are associated with reduced risk of bladder cancer for women. Further studies are needed to clarify whether these results reflect causal processes and potential underlying mechanisms.

Designing Dietary Recommendations Using System Level Interactomics Analysis and Network-Based Inference

Background: A range of computational methods that rely on the analysis of genome-wide expression datasets have been developed and successfully used for drug repositioning. The success of these methods is based on the hypothesis that introducing a factor (in this case, a drug molecule) that could reverse the disease gene expression signature will lead to a therapeutic effect. However, it has also been shown that globally reversing the disease expression signature is not a prerequisite for drug activity. On the other hand, the basic idea of significant anti-correlation in expression profiles could have great value for establishing diet-disease associations and could provide new insights into the role of dietary interventions in disease. Methods: We performed an integrated analysis of publicly available gene expression profiles for foods, diseases and drugs, by calculating pairwise similarity scores for diet and disease gene expression signatures and characterizing their topological features in protein-protein interaction networks. Results: We identified 485 diet-disease pairs where diet could positively influence disease development and 472 pairs where specific diets should be avoided in a disease state. Multiple evidence suggests that orange, whey and coconut fat could be beneficial for psoriasis, lung adenocarcinoma and macular degeneration, respectively. On the other hand, fructose-rich diet should be restricted in patients with chronic intermittent hypoxia and ovarian cancer. Since humans normally do not consume foods in isolation, we also applied different algorithms to predict synergism; as a result, 58 food pairs were predicted. Interestingly, the diets identified as anti-correlated with diseases showed a topological proximity to the disease proteins similar to that of the corresponding drugs. Conclusions: In conclusion, we provide a computational framework for establishing diet-disease associations and additional information on the role of diet in disease development. Due to the complexity of analyzing the food composition and eating patterns of individuals our in silico analysis, using large-scale gene expression datasets and network-based topological features, may serve as a proof-of-concept in nutritional systems biology for identifying diet-disease relationships and subsequently designing dietary recommendations.

Association between GWAS-identified lung adenocarcinoma susceptibility loci and EGFR mutations in never-smoking Asian women, and comparison with findings from Western populations

To evaluate associations by EGFR mutation status for lung adenocarcinoma risk among never-smoking Asian women, we conducted a meta-analysis of 11 loci previously identified in genome-wide association studies (GWAS). Genotyping in an additional 10,780 never-smoking cases and 10,938 never-smoking controls from Asia confirmed associations with eight known single nucleotide polymorphisms (SNPs). Two new signals were observed at genome-wide significance (P < 5 × 10-8), namely, rs7216064 (17q24.3, BPTF), for overall lung adenocarcinoma risk, and rs3817963 (6p21.3, BTNL2) which is specific to cases with EGFR mutations. In further sub-analyses by EGFR status, rs9387478 (ROS1/DCBLD1) and rs2179920 (HLA-DPB1) showed stronger estimated associations in EGFR-positive compared to EGFR-negative cases. Comparison of the overall associations with published results in Western populations revealed that the majority of these findings were distinct, underscoring the importance of distinct contributing factors for smoking and non-smoking lung cancer. Our results extend the catalogue of regions associated with lung adenocarcinoma in non-smoking Asian women and highlight the importance of how the germline could inform risk for specific tumour mutation patterns, which could have important translational implications.

Association of variations in HLA class II and other loci with susceptibility to EGFR-mutated lung adenocarcinoma

Lung adenocarcinoma driven by somatic EGFR mutations is more prevalent in East Asians (30–50%) than in European/Americans (10–20%). Here we investigate genetic factors underlying the risk of this disease by conducting a genome-wide association study, followed by two validation studies, in 3,173 Japanese patients with EGFR mutation-positive lung adenocarcinoma and 15,158 controls. Four loci, 5p15.33 (TERT), 6p21.3 (BTNL2), 3q28 (TP63) and 17q24.2 (BPTF), previously shown to be strongly associated with overall lung adenocarcinoma risk in East Asians, were re-discovered as loci associated with a higher susceptibility to EGFR mutation-positive lung adenocarcinoma. In addition, two additional loci, HLA class II at 6p21.32 (rs2179920; P =5.1 × 10⁻¹⁷, per-allele OR=1.36) and 6p21.1 (FOXP4) (rs2495239; P=3.9 × 10⁻⁹, per-allele OR=1.19) were newly identified as loci associated with EGFR mutation-positive lung adenocarcinoma. This study indicates that multiple genetic factors underlie the risk of lung adenocarcinomas with EGFR mutations.

EGFR mutations in lung adenocarcinoma are more frequent in East Asians compared to other populations. Here, the authors carry out a genome-wide association study in EGFR mutant cancers and identify loci that are associated with risk of developing this molecular subtype of cancer.

Risk of lung cancer and consumption of vegetables and fruit in Japanese: A pooled analysis of cohort studies in Japan

International reviews have concluded that consumption of fruit and vegetables might decrease the risk of lung cancer. However, the relevant epidemiological evidence still remains insufficient in Japan. Therefore, we performed a pooled analysis of data from four population-based cohort studies in Japan with >200 000 participants and >1700 lung cancer cases. We computed study-specific hazard ratios by quintiles of vegetable and fruit consumption as assessed by food frequency questionnaires. Summary hazard ratios were estimated by pooling the study-specific hazard ratios with a fixed-effect model. In men, we found inverse associations between fruit consumption and the age-adjusted and area-adjusted risk of mortality or incidence of lung cancer. However, the associations were largely attenuated after adjustment for smoking and energy intake. The significant decrease in risk among men remained only for a moderate level of fruit consumption; the lowest summary hazard ratios were found in the third quintile of intake (mortality: 0.71, 95% confidence interval 0.60–0.84; incidence: 0.83, 95% confidence interval 0.70–0.98). This decrease in risk was mainly detected in ever smokers. Conversely, vegetable intake was positively correlated with the risk of incidence of lung cancer after adjustment for smoking and energy intake in men (trend P, 0.024); the summary hazard ratio for the highest quintile was 1.26 (95% confidence interval 1.05–1.50). However, a similar association was not detected for mortality from lung cancer. In conclusion, a moderate level of fruit consumption is associated with a decreased risk of lung cancer in men among the Japanese population.

Soy food consumption and lung cancer risk: a meta-analysis using a common measure across studies

A published meta-analysis pooled individual studies by using the study-specific odds ratio (OR) or relative risk (RR) for the highest vs. lowest category of soy or isoflavone intake from each study, but it should be problematic to make comparison between studies/populations for lung cancer risk as the quantiles are so different from different studies/populations. Therefore, we conducted a meta-analysis to explore the association between exposure of estimated daily soy protein intake in grams and lung cancer risk. We extracted ORs or RRs and 95% confidence intervals (CIs), converted them to the estimated ones for daily soy protein intake and pooled them using fixed or random effects models from 11 epidemiologic studies. Overall, the inverse association between daily grams of soy protein intake and risk of lung cancer was borderline statistically significant (OR = 0.98, 95% CI = 0.96 to 1.00); the inverse association was statistically significant in nonsmokers (OR = 0.96; 95% CI = 0.93 to 0.99) and stronger than in smokers (P for difference <0.05). No statistical significance for the associations was observed between genders, the origin of the participants, study design and types of soy intake. This study suggests a borderline reduction in risk of lung cancer with daily soy protein intake in grams, and a significant inverse association in nonsmokers.

Simultaneous inhibition of cell-cycle, proliferation, survival, metastatic pathways and induction of apoptosis in breast cancer cells by a phytochemical super-cocktail: genes that underpin its mode of action

Traditional chemotherapy and radiotherapy for cancer treatment face serious challenges such as drug resistance and toxic side effects. Complementary / Alternative medicine is increasingly being practiced worldwide due to its safety beneficial therapeutic effects. We hypothesized that a super combination (SC) of known phytochemicals used at bioavailable levels could induce 100% killing of breast cancer (BC) cells without toxic effects on normal cells and that microarray analysis would identify potential genes for targeted therapy of BC. Mesenchymal Stems cells (MSC, control) and two BC cell lines were treated with six well established pro-apoptotic phytochemicals individually and in combination (super cocktail), at bioavailable levels. The compounds were ineffective individually. In combination, they significantly suppressed BC cell proliferation (>80%), inhibited migration and invasion, caused cell cycle arrest and induced apoptosis resulting in 100% cell death. However, there were no deleterious effects on MSC cells used as control. Furthermore, the SC down-regulated the expression of PCNA, Rb, CDK4, BcL-2, SVV, and CD44 (metastasis inducing stem cell factor) in the BC cell lines. Microarray analysis revealed several differentially expressed key genes (PCNA, Rb, CDK4, Bcl-2, SVV, P53 and CD44) underpinning SC-promoted BC cell death and motility. Four unique genes were highly up-regulated (ARC, GADD45B, MYLIP and CDKN1C). This investigation indicates the potential for development of a highly effective phytochemical combination for breast cancer chemoprevention / chemotherapy. The novel over-expressed genes hold the potential for development as markers to follow efficacy of therapy.

Soybean isoflavone genistein regulates apoptosis through NF-κB dependent and independent pathways

Cyclooxygenase-2 (COX-2), the key enzyme of the conversion of arachidonic acid to prostaglandins is an important regulator of inflammation and perhaps apoptosis. Genistein is an active component of legumes and other related food associated with prevention of degenerative diseases possibly through modulating certain signaling pathways. It was investigated whether the induction of apoptosis with genistein was carried out via COX-2 suppression through the regulation of NF-κB. The cox-2 positive and negative cells were used to compare the effect of genistein on the modulation of NF-κB in COX-2 expressed or non-expressed genotypic systems. Suppression of COX-2 as well as decreasing NF-κB DNA binding activity was accompanied with the induction of apoptosis in genistein-treated COX-2 expressed cells. However, in cox-2 negative cells, apoptosis occurred without any involvement of NF-κB with genistein treatement. Genistein induced apoptosis through the generation of reactive oxygen species (ROS) both of cox-2 positive and negative cells. These results suggested that genistein is capable of exihibiting NF-κB-dependent and NF-κB-independent apoptotic control via ROS generation depending on genetic cell types.

EGFR exon 19 in-frame deletion and polymorphisms of DNA repair genes in never-smoking female lung adenocarcinoma patients

We explored potential associations between genetic polymorphisms in genes related to DNA repair and detoxification metabolism and epidermal growth factor receptor (EGFR) mutations in a cohort of 410 never-smoking patients with lung adenocarcinoma. Multivariate-adjusted odds ratios (aORs) and corresponding 95% confidence intervals (CI) of EGFR mutation status in association with the genotypes of DNA repair and detoxification metabolism genes were evaluated using logistic regression analysis. We found an association between in-frame deletion in EGFR exon 19 and a single nucleotide polymorphism (SNP) rs1800566C/T located in NQO1 (aOR, 2.2 with 95% CI, 1.0-4.8) in female never-smokers. The SNP rs744154C/G in ERCC4 was also associated with the EGFR exon 19 in-frame deletion both in never-smokers (aOR, 1.7 with 95% CI, 1.0-3.0) and female never-smokers (aOR, 1.9 with 95% CI, 1.0-3.6). Although the association was marginally significant in multivariate logistic regression analysis, the A/A genotype of rs1047840 in EXO1 was associated with a 7.6-fold increase in the occurrence of the EGFR exon 19 in-frame deletion in female never-smokers. Moreover, risk alleles in NQO1, ERCC4 and EXO1 were associated with an increasing aOR of the EGFR exon 19 in-frame deletion both in never-smokers (p = 0.007 for trend) and female never-smokers (p = 0.002 for trend). Our findings suggest that the in-frame deletion in EGFR exon 19 is associated with polymorphisms in DNA repair and detoxification metabolism genes in never-smoking lung adenocarcinoma patients, especially in females.

Isoflavones inhibit the clonogenicity of human colon cancer cells

Isoflavones are a class of polyphenols that contain various substituents such as hydroxy, methoxy, and glycosyl groups. Methoxy groups are known to increase cell permeability and stability, but small structural changes can result in large differences in biological activity. In this study, the anticancer activities of several methoxy isoflavones were tested using a clonogenic survival assay. The relationship between structural properties of methoxy isoflavones and their anticancer activities on HCT116 colon cancer cell lines were studied quantitatively using comparative molecular field analysis and comparative molecular similarity indices analysis. The purpose of this study was to identify structural changes in isoflavones that increase the inhibitory effect on HCT116 colon cancer cell clonogenicity.

Soy intake is associated with lower lung cancer risk: results from a meta-analysis of epidemiologic studies

BACKGROUND

Although several in vitro and animal in vivo studies have suggested that soy or soy isoflavones may exert inhibitory effects on lung carcinogenesis, epidemiologic studies have reported inconclusive results on the association between soy intake and lung cancer.

OBJECTIVE

The aim of this meta-analysis was to investigate whether an association exists between soy and lung cancer in epidemiologic studies.

DESIGN

We searched PubMed, EMBASE, and the Cochrane Library from their inception to February 2011 for both case-control and cohort studies that assessed soy consumption and lung cancer risk. Study-specific risk estimates were combined by using fixed-effect or random-effect models.

RESULTS

A total of 11 epidemiologic studies that consisted of 8 case-control and 3 prospective cohort studies were included. A significantly inverse association was shown between soy intake and lung cancer with an overall RR of 0.77 (95% CI: 0.65, 0.92). Findings were slightly different when analyses were restricted to 5 high-quality studies (RR: 0.70; 95% CI: 0.45, 0.99). In a subgroup meta-analysis, a statistically significant protective effect of soy consumption was observed in women (RR: 0.79; 95% CI: 0.67, 0.93), never smokers (RR: 0.62; 95% CI: 0.51, 0.76), and Asian populations (RR: 0.86; 95% CI: 0.74, 0.98).

CONCLUSIONS

Our findings indicate that the consumption of soy food is associated with lower lung cancer risk. Because of different methods used to assess soy consumption across studies, more well-designed cohort studies or intervention studies that use unified measures of soy intake are needed to fully characterize such an association.

Risks and benefits of dietary isoflavones for cancer

A high intake of fruits and vegetables is associated with a lower risk of cancer. In this context, considerable attention is paid to Asian populations who consume high amounts of soy and soy-derived isoflavones, and have a lower risk for several cancer types such as breast and prostate cancers than populations in Western countries. Hence, interest focuses on soyfoods, soy products, and soy ingredients such as isoflavones with regard to their possible beneficial effects that were observed in numerous experiments and studies. The outcomes of the studies are not always conclusive, are often contradictory depending on the experimental conditions, and are, therefore, difficult to interpret. Isoflavone research revealed not only beneficial but also adverse effects, for instance, on the reproductive system. This is also the case with tumor-promoting effects on, for example, breast tissue. Isoflavone extracts and supplements are often used for the treatment of menopausal symptoms and for the prevention of age-associated conditions such as cardiovascular diseases and osteoporosis in postmenopausal women. In relation to this, questions about the effectiveness and safety of isoflavones have to be clarified. Moreover, there are concerns about the maternal consumption of isoflavones due to the development of leukemia in infants. In contrast, men may benefit from the intake of isoflavones with regard to reducing the risk of prostate cancer. Therefore, this review examines the risks but also the benefits of isoflavones with regard to various kinds of cancer, which can be derived from animal and human studies as well as from in vitro experiments.

Plasma isoflavones and the risk of lung cancer in women: a nested case-control study in Japan

BACKGROUND

Although several epidemiologic studies have found that isoflavone intake assessed by questionnaire is associated with a decreased risk of lung cancer, no prospective study has investigated this association using blood concentrations of isoflavones.

METHODS

We conducted a nested case-control study within a population-based prospective cohort study. A total of 24,127 women aged 40 to 69 years who returned the baseline questionnaire and provided blood samples were observed from 1990 through 2006. During a median follow-up period of 13.5 years, 126 newly diagnosed lung cancer cases were identified. For each case, we selected two controls matched for age, area, smoking status, and condition of blood draw. A conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs of lung cancer in relation to plasma concentrations of genistein, daidzein, glycitein, equol, and total isoflavones.

RESULTS

After exclusion of 20 lung cancer cases diagnosed in the first 3 years after blood collection, an inverse association was found between plasma genistein concentration and lung cancer risk. The multivariate-adjusted OR (95% CI) of lung cancer in the highest quintile of plasma genistein concentration as compared with that in the lowest quintile was 0.31 (0.12, 0.86; P for trend=0.085). Other isoflavones and total isoflavones were not associated with a significant decrease in the risk of lung cancer.

CONCLUSION

Plasma genistein concentration was inversely associated with lung cancer risk in Japanese women.

IMPACT

Our data support the previously observed association between isoflavone intake and lung cancer risk.

Isoflavone intake and risk of lung cancer: a prospective cohort study in Japan

BACKGROUND

Although case-control studies support the idea that soy foods or isoflavone intake is associated with a decreased risk of lung cancer, little evidence is available from prospective cohort studies. Moreover, no prospective study has addressed this association in men.

OBJECTIVE

We investigated the association between isoflavone intake and lung cancer incidence.

DESIGN

We conducted a population-based prospective cohort study in 36,177 men and 40,484 women aged 45-74 y with no history of cancer at baseline in 1995-1999. Participants responded to a validated questionnaire, which included 138 food items. We used Cox proportional hazards regression analysis to estimate the hazard ratios (HRs) and 95% CIs of lung cancer incidence according to isoflavone intake, which was estimated by genistein content from soy foods.

RESULTS

During 11 y (671,864 person-years) of follow-up, we documented 481 male and 178 female lung cancer cases. In men we found an inverse association between isoflavone intake and risk of lung cancer in never smokers (n = 13,051; multivariate HR in the highest compared with the lowest quartile of isoflavone intake: 0.43; 95% CI: 0.21, 0.90; P for trend = 0.024) but not in current or past smokers. A similar, nonsignificant inverse association was seen in never-smoking women (n = 38,211; HR: 0.67; 95% CI: 0.41, 1.10; P for trend = 0.135). We also tested effect modification by smoking status (P for interaction = 0.085 in men and 0.055 in men and women combined).

CONCLUSION

In a large-scale, population-based, prospective study in Japan, isoflavone intake was associated with a decreased risk of lung cancer in never smokers.

Dietary chemopreventive phytochemicals: too little or too much?

There is a large body of evidence that the consumption of fruit and vegetables can decrease the risk of cancer. However, the link between diet and health is extremely complex. Some dietary phytochemicals seem to offer protection in an exposure-related manner and many molecular targets and signaling pathways affected by phytochemicals have been discovered. Although in vitro studies have contributed significantly to our understanding, quite a number use concentrations orders of magnitude greater than those achievable in humans or toxic to normal tissues (exemplified by toxic concentrations of indole-3-carbinol, epigallocatechin-3-gallate, curcumin, and genistein for breast cells). Such studies may produce results that are physiologically irrelevant, thus hindering predictions of efficacy. Here, we argue for careful consideration to be given to the in vitro experimental conditions under which dietary phytochemicals are investigated. Design features, such as the use of appropriate nontoxic concentrations, extended treatment times, three-dimensional cultures, primary tumor cultures, and comparison of susceptibility of various cancer subtypes, should improve our understanding of their molecular targets. This in turn would facilitate predictions as to their potential usefulness in the clinic.

Chemopreventive effects of gefitinib on nonsmoking-related lung tumorigenesis in activating epidermal growth factor receptor transgenic mice

Twenty-five percent of all lung cancer cases are not attributable to smoking. Epidermal growth factor receptor (EGFR) mutations, which are involved in approximately 50% of nonsmoker lung cancer, are positively correlated with responsiveness to gefitinib, and inversely correlated with smoking history. Activating EGFR mutations play a critical role in the carcinogenesis of nonsmoking-related lung cancer. To investigate the chemopreventive effects of gefitinib on nonsmoking-related lung cancer, we generated transgenic mice expressing EGFR L858R in type II pneumocytes constitutively using the surfactant protein-C promoter. The transgenic mice invariably developed atypical adenomatous hyperplasia at age 4 weeks and multifocal adenocarcinoma of varying sizes at age 7 weeks. Notably, the expression levels of phosphorylated and total ErbB2, ErbB3, and thyroid transcription factor-1 were elevated in the transgenic mice compared with wild-type controls at age 3 weeks. Administration of gefitinib to 3-week-old transgenic mice for 1 week before carcinogenesis reduced the amount of phosphorylated EGFR in the lungs of the mice to the baseline level. Gefitinib (5 mg/kg/d; n = 5, 5, and 15) or vehicle (n = 5, 5, and 15) was administered to transgenic mice from age 3 to 8, 13, and 18 weeks, respectively. The numbers of lung tumors in the control and gefitinib-treated groups were 1.75, 5.8, 10.2, and 0 (P < 0.05), respectively. No fatal toxic events occurred in either group, and gefitinib inhibited tumorigenesis completely in this mouse model. These results suggest the utility of molecular targeted chemoprevention against nonsmoking-related lung cancer.

NAT2 fast acetylator genotypes are associated with an increased risk for lung cancer with wildtype epidermal growth factor receptors in Taiwan

Identifying the risk factors responsible for lung cancer especially for nonsmokers is critical for both its prevention and treatment. Studies have linked the polymorphisms in N-acetyltransferases (NAT2), a key enzyme for metabolism of hydrocarbons, with lung cancer in Asian female nonsmokers. Since a high percentage of lung adenocarcinoma in Asian female nonsmokers contains activating hotspot mutations in epidermal growth factor receptors (EGFR), we hypothesized that NAT2 polymorphisms might represent a risk factor in lung cancer with EGFR mutations. We studied NAT polymorphisms in 117 nonsmall cell lung cancer (NSCLC) patients and in 119 healthy controls and EGFR hotspot mutations in exons 18-21 in 100 of the 117 patients using polymerase chain reactions. NAT2 fast acetylator genotypes were significantly associated with patients with lung cancer (P = 0.04, odds ratio (OR): 1.90, 95% confidence interval (CI): 1.02-3.57). Further analyses revealed that NAT2 fast acetylator genotypes were significantly associated with NSCLC with wildtype EGFR (P = 0.008, OR: 3.16, 95% CI: 1.31-7.63), but not with those with EGFR mutations (P = 0.40). Therefore, NAT2 fast acetylator genotypes are a potential risk factor especially for lung cancer with wildtype EGFR.