Chemoprevention of Breast cancer

Breast cancer remains very common disease among women with a global incidence of over 2 million cases per year and is responsible for the highest number of cancer-related deaths among women (1,2). The limitations of current treatment strategies include resistance to drug treatment, significant side effects and cost. The high incidence and limitations on therapeutic strategies underscore the importance of pursuing prevention strategies that lack significant adverse effects. Numerous dietary components and vitamins have been studied extensively as anticancer agents have been found to inhibit the molecular events and signalling pathways associated with various stages of breast cancer development and therefore are useful in breast cancer chemoprevention. It should be highlighted that cooking destroys almost two thirds of vitamins and micronutrients. We have reviewed extensive literature published to date and selected vitamins and micronutrients that have the highest levels of consistent evidence. Read more about vitamins and micronutrients that may help protect against breast cancer in this peer reviewed article:

It has been demonstrated that treating breast cancer cells with 1,25(OH)D3 induces two beneficial effects: an anti-proliferative effect suppressing growth of cells (3) and a pro-apoptotic effect encouraging natural breast cancer cells death (4).

A recent meta-analysis of 68 studies published in 2018 (51 case-control and 17 cohort studies) showed a protective effect between 25 (OH) vitamin D and breast cancer with a 35% reduction in risk observed in case-control studies and 15% risk reduction in cohort studies. However, analysing by menopausal status, the protective vitamin D – breast cancer association persisted only in the premenopausal group (33% risk reduction) when restricting the analysis to nested case-control studies (5).

A more recent meta-analysis has demonstrated that vitamin D deficiency was directly related to breast cancer risk while total blood vitamin D levels and supplemental vitamin D intakes had a protective effect (6).

A dose-response meta-analysis of six cohort studies explored relationships between circulating vitamin D levels and overall survival in 5984 breast cancer patients found a highly significant linear dose-response association between circulating vitamin D levels and overall survival in those patients (7). Finally, a meta-analysis of five studies including 4413 breast cancer patients showed that higher 25(OH) vitamin D levels (>75nmol/L) were associated with a 42% reduction in the odds of dying from breast cancer (8).

Vitamin B6 is involved in many biochemical reactions and might play a role in carcinogenesis.  A combined analysis data derived from 5 studies carried out in the United States including 2509 breast cancer cases showed that high serum pyridoxal 5′-phosphate levels (PLP is the active form of vitamin B6) were associated with 20% reduction in breast cancer risk compared with low levels among postmenopausal women (9).

A more comprehensive analysis in 2017 of 121 observational studies (participants = 1 924 506; cancer cases = 96 , 436) and 9 randomized controlled trials (RCTs; participants, n = 34 911; cases, n = 2539) considering 19 tumour sites revealed that high intake of dietary (food only) vitamin B6 was statistically significantly associated with 22% lower risk of all cancers (10).

Vitamin B9 is an essential nutrient that naturally occurs as folate. A pooled analysis of 23 prospective studies involving 41,516 cases of breast cancer and 1,171,048 individuals were included for meta-analysis. Folate intake was found to be associated with an 18% decrease in risk of developing hormone receptor negative breast cancer. An increment of folate intake of 100 micrograms per day was associated with a 10% decrease in risk among women who drink moderate amounts of alcohol (11).

Furthermore, BRCA1 mutation carriers who used any folic acid-containing supplement had a significantly decreased risk of breast cancer (55% risk reduction) compared to women who never used a folic acid-containing supplement (12). Finally, relatively high dietary intake of folate intake was inversely associated with risk of cancer of the womb (48% risk reduction) and ovaries (61% risk reduction) (13). Therefore, it makes sense for women to take a daily folate supplement (400 micrograms daily). This is a healthier form of vitamin B9 than folic acid.

Beta carotene is a precursor for vitamin A and is found predominantly in carrots, mango, maize, lentils, dark green leaves, amaranth, and spinach. A pooled analysis of eight cohort studies comprising more than 80% of the world’s published prospective data on plasma or serum carotenoids and breast cancer, including 3055 case subjects and 3956 matched control subjects revealed that high serum levels of beta carotene were associated a 17% reduction in breast cancer risk (14). Furthermore, a meta-analysis of 10 studies (8 cohort, 1 clinical trial, and 1 of pooled studies), with 19,450 breast cancer cases showed that the dietary intake of β-carotene was significantly associated with improved breast cancer survival with a 30% reduction in the odds of dying from breast cancer (15). In a large prospective analysis with 20 years of follow-up, women with high plasma carotenoids were at reduced breast cancer risk particularly for more aggressive and ultimately fatal disease. Higher concentrations of β-carotene were associated with 28% statistically significantly lower risk of breast cancer (15).

Turmeric is a yellow spice and gives a specific flavour in Asian food. Curcumin, a polyphenolic compound, is a secondary metabolite isolated from turmeric. Despite the lack of evidence from human clinical studies, using curcumin as a therapeutic and preventive agent in breast cancer is supported by the extensive evidence derived from laboratory and animal studies demonstrating diverse biological activity against breast cancer cells and tumours much of which remains inexplicable (16). The anti-breast-cancer effects of curcumin were mainly investigators in animal and laboratory studies.

Curcumin influences breast development and progression through its effect on cell cycle and proliferation, natural cell death, cancer spread and development of new blood supply to support tumour progression (17,18). The key signalling pathways involved include the NFkB, PI3K/Akt/mTOR, MAPK and JAK/STAT (19). Curcumin also mediated modulation of tumour microenvironment, cancer immunity, breast cancer stem cells and cancer related micro RNAs (20). The chemopreventive effect of curcumin towards mammary tumorigenesis was observed in both the initiation and post-initiation phases and was found to significantly inhibit the initiation of mammary adenocarcinoma (21,22).

Concomitant administration of piperine significantly enhances the extent of absorption, serum concentration and bioavailability of curcumin in humans up to 20 folds (23,24). Piperine has also been proved to exert anti breast cancer properties mainly by inhibiting proliferation and promoting apoptosis (25). Piperine was found to downregulate cyclin B1 expression, inhibit hormone-dependent breast cancer cells and strongly suppress epidermal growth factor (EGF)-mediated expression of MMP-9 and MMP-13 in breast cancer cells, which are activated in up to one-third of breast cancer patients, leading to an inhibition of the migration of breast cancer cells (26,27).

In studying the anticancer effect of bioactive phytochemicals combined with conventional cancer therapies, piperine was found to potentiate the cytotoxicity of anti-cancer drugs and even reverse multi-drug resistance, which impairs the efficacy of chemotherapy (28). Piperine can also enhance the sensitisation of HER2-overexpressing breast cancer cells to paclitaxel (Taxol®), a chemotherapy medication used to treat breast cancer (26,29). A synergistic effect was also observed with Tamoxifen against breast cancer cells (30). In triple-negative breast cancer, which is most the aggressive type of breast cancer and is poorly responsive to endocrine therapeutics, piperine was found to increase apoptotic cells via the mitochondrial pathway and augment the effectiveness of TNF-related apoptosis-inducing ligand-based (TRAIL)-based therapeutic (31).

In studying the combination with radiotherapy, piperine enhanced the γ radiation cytotoxicity for triple-negative breast cancer and the combination of piperine and curcumin sensitised breast cancer cells to radiation in dose dependent manner (32,33).

Sulforaphane is an isothiocyanate phytochemical from cruciferous vegetables with multiple molecular targets, anti-inflammatory, anti-oxidant and anti-cancer properties. Researchers have reported several chemopreventive benefits of Sulforaphane consumption.

Studies demonstrated that sulforaphane influences human cancer development and progression through the modulation and/or regulation of cell cycle and key cellular mechanisms such as reductions in tumour growth, induction of cell cycle arrest, activation of programmed cell death and disruption of signalling within tumour microenvironments (34). In human breast cancer, sulforaphane was found to inhibit cell growth, induce G2/M cell cycle block, inhibit cell mitotic progression and tubulin polymerisation, increase expression of cyclin B1, induce oligonucleosomal DNA fragmentation, increase proteasome-mediated degradation, activate apoptosis, inhibit oestrogen receptor alpha expression and decrease the expression of both EGFR and HER2 (35–39).

In the exploration of combination therapy with piperine, sulforaphane was reported to sensitise human breast cancer cells to paclitaxel (Taxol®) and enhanced the activity of doxorubicin (40,41).

Indole-3-carbinol is another phytochemical which is produced by the breakdown of the glucosinolates that are found at relatively high levels in cruciferous vegetables. Indole-3-carbinol has been shown to be a potent chemopreventive agent for hormonal-dependent breast cancer through its ability to selectively induce apoptosis and alter oestrogen metabolism (42–45).

Numerous studies investigating associations of cruciferous vegetables intake with risk of breast cancer have reported that consumption of cruciferous vegetables has a protective effect in breast cancer, which is largely attributed to sulforaphane and Indole-3-carbinol.

A meta-analysis of thirteen epidemiologic studies (11 case-control and 2 cohort studies) has indicated that high consumption of cruciferous vegetables was significantly associated with 15% reduction in breast cancer risk (46). In a more recent study involving 1485 cases and 1506 controls, intake of cruciferous vegetable significantly reduces the breast cancer risk by almost 50% in the Chinese population. The chemoprevention benefit of cruciferous diet is largely attributed to sulforaphane and Indole-3-carbinol (47).

In another case-control study in 1491 patients with breast cancer and 1482 controls, inverse associations with breast cancer risk were also reported for cruciferous vegetable intake which contain high concentrations of glucosinolates that are hydrolysed by the intestinal microflora to isothiocyanates; mainly sulforaphane (48). A meta-analysis of studies conducted over 18 years in Europe included a total of 3034 of breast cancer patients and 11,492 controls showed that consumption of cruciferous vegetables was also inversely related to breast cancer (49).

Furthermore, in a case–control study involving 1,463 cases and 1,500 controls, inverse associations between cruciferous vegetables and breast cancer have been observed, mainly for postmenopausal women with oestrogen receptor (ER)+ tumours (50). Similarly, in another case–control study involving 740 Caucasian women with breast cancer and 810 controls, inverse associations have been reported between consumption of cruciferous vegetables and breast cancer risk, predominantly among premenopausal women (51).

Quercetin is a bioactive flavonoid pigment found in several fruits, vegetables and leaves.  In addition to its free-radical scavenging antioxidant activity, quercetin has been reported to exert potent anti-tumour properties.

Studies suggest that quercetin’s cancer-protecting effects result from triggering TRAIL-mediated cancer cell death and targeting key signalling transducers leading to the restoration of tumour suppressor genes and inhibition of oncogenes expression (52–54). Besides, quercetin was found to reverse epigenetic alterations associated to oncogenes activation and inactivation of tumour suppressor genes (55).

Quercetin successfully reversed multidrug resistance and restored chemosensitivity to cyclophosphamide of human chemo-resistant triple-negative breast cancer cells (56). Also, quercetin was found to augment doxorubicin chemotherapeutic effects against human breast cancer cells and reduce its cytotoxic side effects (doxorubicin is a first-line chemotherapeutic for breast cancer however, its toxic side effects on normal tissues limit its clinical utility) (57,58). Quercetin also inhibited angiogenesis in acquired tamoxifen-resistant breast cancer cells, which is a serious therapeutic problem among breast cancer patients (59).

In a meta-analysis of twelve studies (including 9 513 cases and 181 906 controls, 6 of which were prospective cohort studies, and 6 were case-control studies); The risk of breast cancer was significantly decreased by 12% in women with high intake of flavonols including quercetin compared with that in those with low consumption of it, especially among post-menopausal women (60). In a network of multicentric Italian case-control studies (involving about 10,000 cancer cases and 16,000 controls), a reduced breast cancer risk by 20% was reported for high intake of flavonols such as quercetin (61,62). Similarly, a large Greek case-control study of 820 women with breast cancer and 1548 controls found that women consuming higher levels of flavonols were at a lower risk of developing breast cancer (63). Finally, the Finnish Mobile Clinic Health Examination Survey involving a total of 62 440 individuals with 1093 cancer cases reported that breast cancer risk and occurrence of all cancers combined were significantly lower at higher consumption of quercetin (64).

Green tea has been extensively studied for its potential protective effect from various types of human cancers. Compared to other teas, green tea contains the highest amount of bioactive compounds that belong to the polyphenol group (65). Scientific literature has presented evidence that green tea exerts protective effects against tumorigenesis owing to its principal polyphenol, namely epigallocatechin-3-gallate (EGCG) (66).

Evidence from several laboratory studies has demonstrated the strong chemopreventive and potentially cancer chemotherapeutic effects of the major green tea constituent, epigallocatechin-3-gallate (EGCG), against breast cancer (67). Most experimental data have shown that green polyphenols can modulate multiple signalling pathways and regulate the growth, survival and metastasis of cancer cell at multiple levels (71, 72).

In addition to the inhibition of clonal expansion of cancer stem cells and the modulation of tumour progression by maintaining a quiescent state in cancer cells, green tea (EGCG) can modulate multiple cell signalling pathways implicated in angiogenesis, metastasis and invasion, such as the inhibition of matrix metalloproteinases (MMPs) and the inhibition of vascular endothelial growth factor (VEGF). EGCG has also been reported to inhibit activator protein 1 and MAPKs, cyclo-oxygenase-2 overexpression, proteasome activity, nitric oxide synthesis, HER-2/neu signalling, insulin-like growth factor-1 (IGF-1)-mediated signalling and nuclear factor-κB (NFκ-B) signalling pathways. EGCG has been found to suppress the binding of epidermal growth factor (EGF) to its receptor, leading to the inhibition of EGF-mediated signal transduction pathways (70).

Moreover, previous studies have shown that green tea major constituent (EGCG) can decrease tumorigenicity by inhibiting the formation of DNA adducts, which are alterations in DNA that result from exposure to carcinogens and affect directly the regulation of transcription of oncogenes and/or tumour suppressors (74-77). Green tea polyphenols can also downregulate oncogenes and upregulate tumour-suppressor genes via modulating multiple epigenetic events (75). Data from in-vitro and in-vivo studies have shown that green tea polyphenols can induce programmed cell death in breast cancer cells either by a preferential cancer-specific induction of reactive oxygen species (ROS) or by epigenetic modulation of expression of apoptosis-related genes, such as human telomerase reverse transcriptase (hTERT) (76–78).

A meta-analysis of breast cancer incidence and recurrence involving 5,617 cases of breast cancer, has shown that green tea consumption is inversely associated with the risk of breast cancer recurrence. When only the case-control studies of breast cancer incidence were examined, the inverse association was maintained (79). In line with the previous meta-analysis, a more recent systematic review and meta-analysis of several observational studies encompassing 163,810 people, has reported a statistically significant inverse relationship between green tea consumption and breast cancer risk with a reduction of risk by 15%. When only the case-control studies were analysed, the protective effect observed was even higher, being 19% reduction in breast cancer risk. The significance of case-control studies in defining the causal relationship between exposure and event cannot be overemphasised. Finally, in a sensitivity analysis of the studies with high quality scores included in this meta-analysis, the reduction of breast cancer risk reported was even higher, at 27% (80).

Epidemiological studies indicated that the relatively higher incidence of breast cancer in developed countries in Western Europe and North America compared to the Inuit and the Japanese can explained by the variation in dietary patterns, in particular variations concerning intake of fatty fish and fat from marine mammals, which may be key modifiers of breast cancer risk (81–83). This preventive effect towards breast cancer has been attributed to the very high dietary intake of marine polyunsaturated fatty acids (PUFAs), mainly omega-3 PUFAs (n-3 PUFA) and omega-6 PUFAs (n-6 PUFA), found in fatty cold-water fish and fat from marine mammals (84).

The protective effect of polyunsaturated fatty acids against breast carcinogenesis was supported by multiple animal experiments and in vitro studies (85–88). Current evidence from experimental studies has shown that ratio of n-3/n-6 PUFAs can reduce the amount of proinflammatory lipid derivatives, growth factor receptor signalling, the NF-κB mediated cytokine production, and can modulate the signal transduction mediated by the mammalian target of rapamycin (mTOR) and the growth of breast cancer cells, by competing for cyclooxygenase and lipoxygenase metabolic pathway (89). However, the precise molecular mechanism by which these marine PUFAs can affect carcinogenesis and angiogenesis of breast cancer remains to be unequivocally defined.

In order to examine the association between the risk of breast cancer and dietary n-3 PUFA intake, a meta-analysis of data from 21 independent prospective cohort studies involving 20,905 breast cancer events and 883,585 participants was performed. Higher consumption of n-3 PUFA has been reported to be associated with a 14% reduction in breast cancer risk. This relative risk was independent of whether n-3 PUFA is measured as dietary intake or as tissue biomarkers. The dose-response analysis showed that risk of breast cancer can decrease by a 5% per 0.1g/day increment of dietary n-3 PUFA intake (90).

To quantitatively ascertain the relationship between the risk of breast cancer and high intake ratios of n-3/n-6 PUFAs, a meta-analysis of five cohort studies and six prospective nested case-control studies, involving 8,331 cases of breast cancer from 274,135 adult females from several countries was performed. Among study populations, individuals with higher dietary intake ratios of the omega‐3 to omega‐6 (PUFAs) were reported to have a significantly reduced risk of breast cancer. When the dose-response association was analysed, an increment per 1/10 of n-3/n-6 (PUFAs) ratio in diet was associated with a further 6% reduction of breast cancer risk. More importantly, the subgroup analysis has shown that individuals in 3 studies from USA with higher intake ratios of n-3/n-6 in serum phospholipids had a 38% reduction of breast cancer risk. When the dose-response association was evaluated as above, an increment per 1/10 of serum phospholipids of omega‐3 to omega‐6 (PUFAs) ratio was associated with a 27% reduction of breast cancer risk. As EPA and DHA cannot be synthesised de novo in mammals and inter-conversion between n-3 and n-6 polyunsaturated fatty acids does not exist in humans, serum phospholipids of omega‐3 to omega‐6 (PUFAs) ratios reflect their dietary intake ratios (91).

Alpha-linolenic acid, which is one of the most abundant omega-3 polyunsaturated fatty acid in typical Western diets, is metabolised to two long-chain n-3 PUFAs, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (92). Typical consumption of alpha-linolenic acid among Western adults is in the range of 0.5–2 g/d which is approximately 15- and 25-fold higher than of DHA and EPA, respectively (93–97). As human conversion of alpha-linolenic acid to its longer-chain derivatives EPA & DHA is inefficient, very high intakes of alpha-linolenic acid are required to allow sufficient synthesis of its longer-chain derivatives EPA & DHA (99, 101). While the total percentage of conversion of alpha-linolenic acid to EPA & DHA varies widely, ranging from 5–18.5%, it has been reported that 2.8% of dietary alpha-linolenic acid consumed is converted to EPA and that less than 1–4% of dietary alpha-linolenic acid is converted to DHA (102, 103). Furthermore, although the relationship between increased alpha-linolenic acid intake and increased EPA concentration in plasma and tissue lipids is linear, several studies revealed a tendency for DHA to decline when alpha-linolenic acid consumption is markedly increased (96). Moreover, the recent increased intake of linoleic acid, which is the main polyunsaturated fatty acid in most Western diets and is typically consumed in 5- to 20-fold greater amounts than alpha-linolenic acid, has been found to decrease tissue concentrations of EPA and DHA (100, 104). Additionally, the choice of cooking oil and cooking method (particularly deep frying) can also qualitatively and quantitatively influence the total fatty acid content in cooked fish  (102,103).

The limited conversion from dietary alpha-linolenic acid and the increased consumption of linoleic acid as well as the variation in choice of cooking method imply that protective breast tissue levels of EPA & DHA can be achieved only by direct consumption of these polyunsaturated fatty acids (105, 106). It has been evidenced that omega-3 supplementation reaches and imparts significant improvements in the ratio of n-3/n-6 PUFAs at the target breast tissue (106). This justifies a reconsideration of the dietary reference intake for EPA & DHA and provides solid and robust evidence that supports breast cancer prevention by increasing consumption of dietary intake ratios of n-3/n-6 PUFAs.

There is sufficient evidence from in vitro, animal and epidemiological human studies that certain vitamins (namely vitamin D3, vitamin B6, folate and beta carotene) and dietary micronutrients (namely curcumin, piperine, sulforaphane, indole-3-carbinol, quercetin, epigallocatechin gallate (EGCG) and omega-3 polyunsaturated fatty acids) display activity against breast cancer and have the potential to offer a natural strategy for breast cancer chemoprevention and reducing the risk of breast cancer recurrence. Therefore, we have designed a supplement (OncoMute) that contains most of these micronutrients using the safest form and dosage.