Drug repurposing provides a cost-effective approach to address the need for breast cancer prevention and therapeutics. We aimed to identify actionable druggable targets using Mendelian randomization (MR) and then validate the candidate drugs using population-based analyses. We identified genetic instruments for 1406 actionable targets of approved non-oncological drugs based on gene expression, DNA methylation, and protein expression quantitative trait loci (eQTL, mQTL, and pQTL, respectively). Genome-wide association study (GWAS) summary statistics were obtained from the Breast Cancer Association Consortium (122,977 cases, 105,974 controls). We further conducted a nested case–control study using data retrieved from Swedish registers to validate the candidate drugs that were identified from MR analyses. We identified six significant MR associations with gene expression levels (TUBB, MDM2, CSK, ULK3, MC1R and KCNN4) and two significant associations with gene methylation levels across 21 CpG islands (RPS23 and MAPT). Results from the nested case–control study showed that the use of raloxifene (targeting MAPT) was associated with 35% reduced breast cancer risk (odds ratio, OR, 0.65; 95% confidence interval, CI, 0.51–0.83). However, usage of estradiol, tolterodine, and nitrofurantoin (also targeting MAPT) was associated with increased breast cancer risk, with adjusted ORs and 95% CI of 1.10 (1.07–1.13), 1.16 (1.09–1.24), and 1.09 (1.05–1.13), respectively. The effect of raloxifene and nitrofurantoin lost significance in further validation analyses using active-comparator and new-user design. This large-scale MR analysis, combined with population-based validation, identified eight druggable target genes for breast cancer and suggested that raloxifene is an effective chemoprevention against breast cancer. 10.13039/501100004359 Swedish Research Council , 10.13039/501100002794 Cancerfonden , 10.13039/501100003173 Crafoordska Stiftelsen , Allmänna Sjukhusets i Malmö Stiftelsen för bekämpande av cancer, 10.13039/501100013314 111 Project and MAS cancer.

This study aimed to explore the effect of dietary magnesium intake on breast cancer risk both directly and indirectly via its effect on inflammatory markers C-reactive protein (CRP) and interleukin-6 (IL-6). This case-control study recruited 1050 case patients and 1229 control subjects. Inflammatory marker levels of 322 cases and 322 controls, randomly selected, were measured using ELISA, and data on dietary magnesium intake were collected using a food frequency questionnaire. Multivariable logistic regression was used to estimate the odds ratio (OR) and 95% confidence interval (CI), and path analysis was used to investigate the mediating effect. A higher magnesium intake was associated with a lower breast cancer risk (adjusted OR = 0.80, 95% CI = 0.65, 0.99). A positive association was found between the CRP level and breast cancer risk (adjusted OR = 1.43, 95% CI = 1.02–2.01). However, IL-6 was not found to be associated with breast cancer risk. Path analysis revealed that dietary magnesium affected breast cancer risk both directly and indirectly by influencing the CRP level. The results indicate that a direct negative association and an indirect association through influencing the CRP level were observed between dietary magnesium intake and breast cancer risk.

Anti-tumor effect of dietary flavonoids has been sustained by laboratory experiments, but epidemiological studies with breast cancer risk remained inconsistent and insufficient. This study aimed to investigate the associations between total and subclasses of flavonoid and breast cancer risk among Chinese population. This case-control study recruited 1522 eligible breast cancer cases and 1547 frequency-matched control subjects from June 2007 to July 2018 in Guangdong, China. Dietary intake was obtained by face-to-face interview using a validated food frequency questionnaire. Odds ratios and 95% confidence intervals were calculated by multivariable logistic regression models. After adjusting for potential confounders, inverse associations were observed between total flavonoids, anthocyanidins, proanthocyanidins, flavanones, flavones, flavonols and isoflavones and overall breast cancer risk. Comparing the highest versus the lowest quartile, odds ratio (95% confidence interval) was 0.66 (0.54–0.82) for total flavonoids, 0.61 (0.49–0.75) for anthocyanidins, 0.67 (0.54–0.83) for proanthocyanidins, 0.71 (0.57–0.88) for flavanones, 0.48 (0.39–0.60) for flavones, 0.51 (0.41–0.63) for flavonols and 0.67 (0.54–0.83) for isoflavones, respectively. No significant association was found between flavanols, flavan-3-ol monomers, theaflavins and breast cancer risk. Stratified analysis by menopausal status and estrogen receptor/progesterone receptor status showed that the associations of total flavonoids, most flavonoid subclasses with breast cancer risk were generally not modified by menopausal or estrogen receptor/progesterone receptor status. This study indicates that total flavonoids and most flavonoid subclasses intakes were inversely associated with breast cancer risk.

Although previous studies have investigated the association of cruciferous vegetable consumption with breast cancer risk, few studies focused on the association between bioactive components in cruciferous vegetables, glucosinolates (GSL) and isothiocyanates (ITC), and breast cancer risk. This study aimed to examine the association between consumption of cruciferous vegetables and breast cancer risk according to GSL and ITC contents in a Chinese population. A total of 1485 cases and 1506 controls were recruited into this case–control study from June 2007 to March 2017. Consumption of cruciferous vegetables was assessed using a validated FFQ. Dietary GSL and ITC were computed by using two food composition databases linking GSL and ITC contents in cruciferous vegetables with responses to the FFQ. The OR and 95 % CI were assessed by unconditional logistic regression after adjusting for the potential confounders. Significant inverse associations were found between consumption of cruciferous vegetables, GSL and ITC and breast cancer risk. The adjusted OR comparing the highest with the lowest quartile were 0·51 (95 % CI 0·41, 0·63) for cruciferous vegetables, 0·54 (95 % CI 0·44, 0·67) for GSL and 0·62 (95 % CI 0·50, 0·76) for ITC, respectively. These inverse associations were also observed in both premenopausal and postmenopausal women. Subgroup analysis by hormone receptor status found inverse associations between cruciferous vegetables, GSL and ITC and both hormone-receptor-positive or hormone-receptor-negative breast cancer. This study indicated that consumption of cruciferous vegetables, GSL and ITC was inversely associated with breast cancer risk among Chinese women.

The effects of dietary vitamin D, Ca and dairy products intakes on colorectal cancer risk remain controversial. The present study investigated the association between these dietary intakes and the risk of colorectal cancer in Guangdong, China. From July 2010 to December 2018, 2380 patients with colorectal cancer and 2389 sex- and age-matched controls were recruited. Dietary intake data were collected through face-to-face interviews using a validated FFQ. Unconditional multivariable logistic regression models were used to calculate the OR and 95 % CI after adjusting for various confounders. Higher dietary vitamin D and Ca intakes were associated with 43 and 52 % reductions in colorectal cancer risk, with OR of 0·57 (95 % CI 0·46, 0·70) and 0·48 (95 % CI 0·39, 0·61), respectively, for the highest quartile (v. the lowest quartile) intakes. A statistically significant inverse association was observed between total dairy product intake and colorectal cancer risk, with an adjusted OR of 0·32 (95 % CI 0·27, 0·39) for the highest v. the lowest tertile. Subjects who drank milk had a 48 % lower risk of colorectal cancer than those who did not (OR 0·52, 95 % CI 0·45, 0·59). The inverse associations of dietary vitamin D, Ca, total dairy products and milk intakes with the risk of colorectal cancer were independent of sex and cancer site. Our study supports the protective effects of high dietary vitamin D, Ca and dairy products intakes against colorectal cancer in a Chinese population.

Few studies have examined the association of various types of Fe with colorectal cancer risk. The aim of this study was to investigate different forms and sources of Fe in relation to colorectal cancer risk in a Chinese population. A total of 2138 patients with colorectal cancer and 2144 sex- and age-matched (5-year interval) controls were recruited from July 2010 to November 2017. Dietary information was assessed by face-to-face interviews using a validated FFQ. Multivariable logistic regression was used to estimate the OR and 95 % CI on models. Intake of Fe from plants and Fe from white meat were inversely associated with the risk of colorectal cancer, while haem Fe and Fe from red meat were positively associated with colorectal cancer risk. The multivariable OR for the highest quartilev.the lowest quartile were 0·72 (95 % CI 0·59, 0·87,P_trend<0·001) for Fe from plants, 0·54 (95 % CI 0·45, 0·66,P_trend<0·001) for Fe from white meat, 1·26 (95 % CI 1·04, 1·53,P_trend=0·005) for haem Fe and 1·83 (95 % CI 1·49, 2·24,P_trend<0·001) for Fe from red meat intake, respectively. However, no significant association was found between the consumption of total dietary Fe, non-haem Fe, Fe from meat and colorectal cancer risk. This study showed that lower intake of Fe from plants and white meat, as well as higher intake of haem Fe and Fe from red meat, were associated with colorectal cancer risk in a Chinese population.