Correlation between nutritional biomarkers and breast cancer: a case-control study

An Update on Tamoxifen and the Chemo-Preventive Potential of Vitamin E in Breast Cancer Management

Breast cancer (BC) is the most common female cancer in terms of incidence and mortality worldwide. Tamoxifen (Nolvadex) is a widely prescribed, oral anti-estrogen drug for the hormonal treatment of estrogen-receptor-positive BC, which represents 70% of all BC subtypes. This review assesses the current knowledge on the molecular pharmacology of tamoxifen in terms of its anticancer and chemo-preventive actions. Due to the importance of vitamin E compounds, which are widely taken as a supplementary dietary component, the review focuses only on the potential importance of vitamin E in BC chemo-prevention. The chemo-preventive and onco-protective effects of tamoxifen combined with the potential effects of vitamin E can alter the anticancer actions of tamoxifen. Therefore, methods involving an individually designed, nutritional intervention for patients with BC warrant further consideration. These data are of great importance for tamoxifen chemo-prevention strategies in future epidemiological studies.

Cadmium exposure and risk of breast cancer: A dose-response meta-analysis of cohort studies

BACKGROUND

Cadmium is a toxic heavy metal that has been implicated in breast cancer etiology, albeit with inconsistent results.

OBJECTIVE

To investigate the shape of the relation between cadmium exposure and breast cancer incidence and mortality in cohort studies.

DATA SOURCES

Following a literature search through April 14, 2020, we carried out a systematic review and dose-response meta-analysis to investigate the shape of the relation between cadmium exposure (assessed either through diet or urine excretion) and disease incidence and mortality.

STUDY ELIGIBILITY CRITERIA

For inclusion, a study had to report incidence or mortality for breast cancer according to baseline cadmium exposure category; be a prospective cohort, case-cohort or nested case-control study with a minimum one-year follow-up, and reporting effect estimates for all exposure categories.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies were evaluated using the ROBINS-E risk of bias tool. The effects in humans were assessed quantitatively using one-stage dose-response meta-analysis in a random effects meta-analytical model.

RESULTS

We identified 10 studies eligible for inclusion in the dose-response meta-analysis, six based on cadmium dietary intake, and four on urinary excretion levels. We found a marginal and imprecise positive relation between dietary cadmium intake and breast cancer, and no association when urinary cadmium excretion was used for exposure assessment. Compared to no exposure, at 20 µg/day of cadmium intake the summary risk ratio was 1.12 (95% confidence interval 0.80-1.56), while at 2 µg/g creatinine of cadmium excretion the summary risk ratio was 0.89 (95% confidence interval 0.38-2.14). Analysis restricted to post-menopausal women showed no association between either dietary or urinary cadmium and subsequent breast cancer incidence and mortality.

LIMITATIONS AND CONCLUSIONS

Overall, we found scant evidence of a positive association between cadmium and breast cancer. Available data were too limited to carry out stratified analyses according to age, smoking and hormone receptor status. Therefore, possible associations between cadmium exposure and breast cancer in selected subgroups cannot be entirely ruled out.

Impact of correlation of predictors on discrimination of risk models in development and external populations

Background

The area under the ROC curve (AUC) of risk models is known to be influenced by differences in case-mix and effect size of predictors. The impact of heterogeneity in correlation among predictors has however been under investigated. We sought to evaluate how correlation among predictors affects the AUC in development and external populations.

Methods

We simulated hypothetical populations using two different methods based on means, standard deviations, and correlation of two continuous predictors. In the first approach, the distribution and correlation of predictors were assumed for the total population. In the second approach, these parameters were modeled conditional on disease status. In both approaches, multivariable logistic regression models were fitted to predict disease risk in individuals. Each risk model developed in a population was validated in the remaining populations to investigate external validity.

Results

For both approaches, we observed that the magnitude of the AUC in the development and external populations depends on the correlation among predictors. Lower AUCs were estimated in scenarios of both strong positive and negative correlation, depending on the direction of predictor effects and the simulation method. However, when adjusted effect sizes of predictors were specified in the opposite directions, increasingly negative correlation consistently improved the AUC. AUCs in external validation populations were higher or lower than in the derivation cohort, even in the presence of similar predictor effects.

Conclusions

Discrimination of risk prediction models should be assessed in various external populations with different correlation structures to make better inferences about model generalizability.

Electronic supplementary material

The online version of this article (doi:10.1186/s12874-017-0345-1) contains supplementary material, which is available to authorized users.

The plasma level of retinol, vitamins A, C and α-tocopherol could reduce breast cancer risk? A meta-analysis and meta-regression

PURPOSE

Plasma antioxidants are supposed to be directly related to breast cancer risk. However, the results remain inconsistent. Herein, we carried this meta-analysis to comprehensively summarize the associations between plasma retinol, vitamins A, C and α-tocopherol and breast cancer risk.

METHODS

We searched PubMed, Embase and the Cochrane Databases (through September 24, 2014) and the reference lists of the retrieved articles in English with sufficient information to estimate relative risk or odds ratio and the 95% confidence intervals (CIs), or with mean serum/plasma level of vitamins and SD/SEM/p value in breast cancer and controls. Two reviewers independently extracted data using a standardized form, with any discrepancy adjudicated by the third reviewer.

RESULTS

Forty studies entered this meta-analysis. For the pooled OR, no significant association between plasma retinol and breast cancer was observed (p = 0.13). Significant association was observed between plasma α-tocopherol and breast cancer (pooled OR 0.42, 95% CI 0.25, 0.72, p = 0.00) in the subgroup with the median lowest level of 5.74-9.16 μmol/L. For the weighted mean difference (WMD), the plasma α-tocopherol and vitamin C level between breast cancer and controls were significantly different [WMD = -0.93 μmol/L (95% CI -1.26, -0.61, p = 0.00) and -2.51 μmol/L (95% CI -4.00, -1.02, p = 0.00), respectively]. No significant association between plasma retinol and vitamin A and breast cancer was observed.

CONCLUSIONS

Severe α-tocopherol deficiency could increase breast cancer risk. The association between plasma vitamin C and breast cancer was only significant in case-control studies. There was no significant association between other vitamins and breast cancer risk.

Aromatase activity induction in human adipose fibroblasts by retinoic acids via retinoic acid receptor α

Estrogen synthesis in adipose tissue is associated with the development of breast cancer. Tumors are preferentially found in breast quadrants with strongest expression of the cytochrome P450 aromatase (encoded by the gene CYP19A1). Several promoters regulated by various hormonal factors drive aromatase expression in human breast adipose fibroblasts (BAFs). As adipose tissue is a major source of retinoids, in this study, we investigated their role in the regulation of aromatase expression. The retinoids all-trans-retinoic acid (at-RA) and 9-cis-RA induce aromatase activity in human BAFs. In BAFs, at-RA induces aromatase gene expression via promoter I.4. In 3T3-L1 cells, both retinoids specifically drive luciferase reporter gene expression under the control of aromatase promoter I.4, whereas other promoters active in human adipose tissue are insensitive. Activation by retinoids depends on a 467 bp fragment (-256/+211) of promoter I.4 containing four putative retinoic acid response elements (RAREs). Site-directed mutagenesis revealed that only RARE2 (+91/+105) mediates the retinoid-dependent induction of reporter gene activity. In 3T3-L1 preadipocytes and human BAFs, RA receptor α (RARα (RARA)) expression is predominant, whereas RARβ (RARB) or RARγ (RARG) expression is low. Electrophoretic mobility shift assays with nuclear extracts obtained from human BAFs and 3T3-L1 cells identified a specific RARE2-binding complex. Retinoids enhanced complex formation, whereas pre-incubation with anti-RARα antibodies prohibited the binding of RARα to RARE2. Chromatin immunoprecipitation showed RA-dependent binding of RARα to the RARE2-containing promoter region in vivo. Furthermore, we provide evidence that RARE2 is also necessary for the basal activation of promoter I.4 in these cells. Taken together, these findings indicate a novel retinoid-dependent mechanism of aromatase activity induction in adipose tissue.

Chemopreventive activity of vitamin E in breast cancer: a focus on γ- and δ-tocopherol

Vitamin E consists of eight different variants: α-, β-, γ-, and δ-tocopherols (saturated phytyl tail) and α-, β-, γ-, and δ-tocotrienols (unsaturated phytyl tail). Cancer prevention studies with vitamin E have primarily utilized the variant α-tocopherol. To no avail, a majority of these studies focused on variant α-tocopherol with inconsistent results. However, γ-tocopherol, and more recently δ-tocopherol, have shown greater ability to reduce inflammation, cell proliferation, and tumor burden. Recent results have shown that γ-enriched mixed tocopherols inhibit the development of mammary hyperplasia and tumorigenesis in animal models. In this review, we discuss the possible differences between the variant forms, molecular targets, and cancer-preventive effects of tocopherols. We recommend that a γ-enriched mixture, γ- and δ-tocopherol, but not α-tocopherol, are promising agents for breast cancer prevention and warrant further investigation.

Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

Uterine leiomyomas express a molecular pattern that lowers retinoic acid exposure

OBJECTIVE

To analyze expression of the retinoic acid signaling pathway genes that are involved in retinol metabolism, transport, transcriptional activation, and transcriptional products in spontaneous human leiomyomas.

DESIGN

Laboratory study of human leiomyoma and patient-matched myometrial tissue.

PATIENT(S)

Eight women undergoing hysterectomy for symptomatic leiomyomas.

INTERVENTION(S)

Confirmation of an altered retinoic acid pathway analyzed by microarray, real time reverse transcription-polymerase chain reaction, Western blot, immunohistochemistry, and high-performance liquid chromatography (HPLC).

MAIN OUTCOME MEASURE(S)

Gene and protein expression.

RESULT(S)

Regardless of patient demographics and leiomyoma location and size, we found decreased expression of the major genes involved in retinoic acid pathway including alcohol dehydrogenase-1 (-3.97- +/- 0.03-fold), aldehyde dehydrogenase-1 (-3.1- +/- 0.07-fold), cellular retinol binding protein-1 (-2.62- +/- 0.04-fold), and cellular retinoic acid binding protein-1 (-2.42- +/- 0.20-fold). Cytochrome P450 (CYP 26A1), which is responsible for retinoic acid metabolism, was highly up-regulated in leiomyomas (+5.4- +/- 0.53-fold). Nuclear receptors demonstrated a complex pattern of under-expression (RARalpha, RARbeta, RXRalpha, RXRgamma) and over-expression (RARgamma, RXRbeta) at both the mRNA and protein level. Differences in protein amounts were confirmed by Western blot. Finally, a reduced amount of cellular ATRA and 9-cis retinoic acid was confirmed by HPLC in leiomyomas compared with myometrial tissues.

CONCLUSION(S)

Molecular alterations in the retinoic acid pathway of leiomyomata result in a decrease in retinoic acid exposure.