Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps

Comparative effectiveness of chemopreventive interventions for colorectal cancer: protocol for a systematic review and network meta-analysis of randomised controlled trials

BACKGROUND

Colorectal cancer (CRC) is the third most common cancer worldwide and is associated with substantial socioeconomic burden. Despite considerable research, including numerous randomised controlled trials (RCTs) and systematic reviews assessed the effect of various chemopreventive interventions for CRC, there remains uncertainty regarding the comparative effectiveness of these agents. No network meta-analytic study has been published to evaluate the efficacies of these agents for CRC. Therefore, the aim of this study is to summarise the direct and indirect evidence for these interventions to prevent CRC in average-high risk individuals, and to rank these agents for practical consideration.

METHODS

We will acquire eligible studies through a systematic search of MEDLINE, EMBASE, the Cochrane Central Registry of Controlled Trials, CINAHL plus, IPA and clinicaltrials.gov website. The Cochrane Risk of Bias Tool will be used to assess the quality of included studies. The primary outcomes are the incidence of CRC, the incidence/recurrence of any adenoma or change in polyp burden (number or size). Quantitative synthesis or meta-analysis will be considered. We will also construct a network meta-analysis (NMA) to improve precision of the comparisons among chemo-preventive interventions by combining direct and indirect evidence. The probability of each treatment being the best and/or safest, the number-needed-to-treat [NNT; 95% credible interval (CrIs)], and the number-needed-to-harm (NNH; 95% CrIs) will be calculated to provide measures of treatment efficacy. The GRADE approach will be used to rate the quality of evidence of estimates derived from NMA.

RESULTS

This protocol has been registered (registration number: CRD42015025849) with the PROSPERO (International Prospective Register of Systematic Reviews). The procedures of this systematic review and NMA will be conducted in accordance with the PRISMA-compliant guideline. The results of this systematic review and NMA will be submitted to a peer-reviewed journal for publication.

CONCLUSIONS

To the best of our knowledge, this study will be the first NMA to identify the comparative effectiveness of interventions for the prevention of CRC. The results of our study will update evidence for chemoprevention of CRC, identify key areas for future research, and provide a framework for conducting large systematic reviews involving indirect comparisons.

Effects of calcium and vitamin D3 on transforming growth factors in rectal mucosa of sporadic colorectal adenoma patients: a randomized controlled trial

Transforming growth factor alpha (TGFα) and TGFβ1 are growth-promoting and -inhibiting autocrine/paracrine growth factors, respectively, that may (1) affect risk for colorectal cancer and (2) be modifiable by anti-proliferative exposures. The effects of supplemental calcium and vitamin D3 on these two markers in the normal-appearing colorectal mucosa in humans are unknown. We conducted a pilot, randomized, double-blind, placebo-controlled, 2 × 2 factorial clinical trial (n = 92; 23/treatment group) of calcium 2 g and/or vitamin D3 800 IU/d versus placebo over 6 mo. TGFα and TGFβ1 expression was measured in biopsies of normal-appearing rectal mucosa using automated immunohistochemistry and quantitative image analysis at baseline and 6-mo follow-up. In the calcium, vitamin D3 , and calcium plus vitamin D3 groups relative to the placebo group (1) the mean overall expression of TGFβ1 increased by 14% (P= 0.25), 19% (P = 0.17), and 22% (P = 0.09); (2) the ratio of TGFα expression in the upper 40% (differentiation zone) to that in the lower 60 (proliferation zone) of the crypts decreased by 34% (P = 0.11), 31% (P = 0.22), and 26% (P = 0.33); and (3) the TGFα/TGFβ1 ratio in the upper 40% of the crypts decreased by 28% (P = 0.09), 14% (P = 0.41), and 22% (P = 0.24), respectively. These preliminary results, although not statistically significant, suggest that supplemental calcium and vitamin D3 may increase TGFβ1 expression and shift TGFα expression downward from the differentiation to the proliferation zone in the crypts in the normal-appearing colorectal mucosa of sporadic colorectal adenoma patients, and support further investigation in a larger clinical trial.

Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and Apc (Min/+) and azoxymethane carcinogen-induced mouse models, to investigate the impact of a western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies.

Risk of colorectal cancer in self-reported inflammatory bowel disease and modification of risk by statin and NSAID use

BACKGROUND

Statins and nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with reduced risk of colorectal cancer (CRC) in some studies. The objective of this study was to quantify the relative risk of inflammatory bowel disease (IBD) as a risk factor for CRC and to estimate whether this risk may be modified by long-term use of NSAIDs or statins.

METHODS

The Molecular Epidemiology of Colorectal Cancer study is a population-based, case-control study of incident colorectal cancer in northern Israel and controls matched by age, sex, clinic, and ethnicity. Personal histories of IBD and medication use were measured by structured, in-person interview. The relative risk of IBD and effect modification by statins and NSAIDs were quantified by conditional and unconditional logistic regression.

RESULTS

Among 1921 matched pairs of CRC cases and controls, a self-reported history of IBD was associated with a 1.9-fold increased risk of CRC (95% confidence interval [CI], 1.12-3.26). Long-term statin use was associated with a reduced risk of both IBD-associated CRC (odds ratio [OR] = 0.07; 95% CI, 0.01-0.78) and non-IBD CRC (OR = 0.49; 95% CI, 0.39-0.62). Stratified analysis suggested that statins may be more protective among those with IBD (ratio of OR = 0.14; 95% CI, 0.01-1.31; P = .51), although not statistically significant. NSAID use in patients with a history of IBD was suggestive of reduced risk of CRC but did not reach statistical significance (OR = 0.47; 95% CI, 0.12-1.86).

CONCLUSIONS

The risk of CRC was elevated 1.9-fold in patients with IBD. Long-term statin use was associated with reduced risk of CRC in patients with IBD.

Chemoprevention for colorectal neoplasia

Colorectal cancer is a major cause of morbidity and mortality in industrialized societies and leads to significant treatment costs. Currently there are screening programs with fecal occult blood testing, radiographic, and endoscopic evaluation. Despite this, mortality from colorectal cancer has not improved dramatically. As such, attention has turned to finding agents to prevent carcinogenesis. The emerging field known as chemoprevention studies agents that target multiple steps in the development of adenomas and their subsequent transformation to colorectal carcinoma. There are multiple case control, cohort, and randomized controlled trials investigating the efficacy of fiber, calcium, vitamin D, folate, and nonsteroidal antiinflammatory drugs as chemopreventive agents against colorectal cancer.

Intake of dairy products and risk of colorectal neoplasia

Prospective cohort studies suggest that higher intakes of dairy products, in particular milk, are associated with a decreased risk of colorectal cancer (CRC). In Western populations, dairy products are major contributors to dietary Ca, which may have chemopreventive effects in the colon. The pooling of data from prospective studies suggests a significant protective effect of Ca on CRC risk. Randomised controlled trials with Ca supplements have been conducted with both colorectal adenoma and CRC as endpoints. Results suggest that Ca supplementation at a level of 1000-2000 mg/d reduces adenoma recurrence in individuals with a previous adenoma but has no effect on CRC incidence. There is evidence that the risk reduction from dairy foods may not be solely due to their high Ca content. Dairy products contain other potential chemopreventive components such as vitamin D, butyric acid, conjugated linoleic acid, sphingolipids, and probiotic bacteria in fermented products such as yoghurt. The present review will focus on the epidemiological evidence (and in particular prospective cohort studies) investigating the relationship between dairy product consumption and risk of CRC. An outline of the proposed mechanisms responsible for the protective effect of both Ca and other potential chemopreventive components in dairy products will also be presented.

Selenium in cancer prevention: a review of the evidence and mechanism of action

Se is an unusual trace element in having its own codon in mRNA that specifies its insertion into selenoproteins as selenocysteine (SeCys), by means of a mechanism requiring a large SeCys-insertion complex. This exacting insertion machinery for selenoprotein production has implications for the Se requirements for cancer prevention. If Se may protect against cancer, an adequate intake of Se is desirable. However, the level of intake in Europe and some parts of the world is not adequate for full expression of protective selenoproteins. The evidence for Se as a cancer preventive agent includes that from geographic, animal, prospective and intervention studies. Newly-published prospective studies on oesophageal, gastric-cardia and lung cancer have reinforced previous evidence, which is particularly strong for prostate cancer. Interventions with Se have shown benefit in reducing the risk of cancer incidence and mortality in all cancers combined, and specifically in liver, prostate, colo-rectal and lung cancers. The effect seems to be strongest in those individuals with the lowest Se status. As the level of Se that appears to be required for optimal effect is higher than that previously understood to be required to maximise the activity of selenoenzymes, the question has been raised as to whether selenoproteins are involved in the anti-cancer process. However, recent evidence showing an association between Se, reduction of DNA damage and oxidative stress together with data showing an effect of selenoprotein genotype on cancer risk implies that selenoproteins are indeed implicated. The likelihood of simultaneous and consecutive effects at different cancer stages still allows an important role for anti-cancer Se metabolites such as methyl selenol formed from γ-glutamyl-selenomethyl-SeCys and selenomethyl-SeCys, components identified in certain plants and Se-enriched yeast that have anti-cancer effects. There is some evidence that Se may affect not only cancer risk but also progression and metastasis. Current primary and secondary prevention trials of Se are underway in the USA, including the Selenium and Vitamin E Cancer Prevention Trial (SELECT) relating to prostate cancer, although a large European trial is still desirable given the likelihood of a stronger effect in populations of lower Se status.

Chemoprevention: risk reduction with medical therapy of inflammatory bowel disease

The ideal chemopreventative agent, in addition to being efficacious in the prevention of cancer, must be easily administered, affordable, safe, and well tolerated, with minimal side effects. In the past decade, a growing body of literature has emerged on the prevention of CRC in patients with long-standing CD and UC. The data are not definitive and consist almost exclusively of retrospective case-control and cohort studies rather than the more rigorous prospective RCTs. 5-ASA compounds have been most thoroughly studied, and most of the existing data support the use of 5-ASA in the prevention of CRC. Although the precise dose and duration are unclear, studies suggest that chronic systemic administration of 5-ASA at a dose of at least 1.2 g/d is most likely to be effective. A beneficial effect of folate, albeit not statistically significant, has been consistently shown in every study performed for this purpose. Folate supplementation, which is safe and affordable, should also be recommended for all patients with IBD, especially those taking sulfasalazine. UDCA has been shown to exert a protective effect in most studies on patients with UC and concomitant PSC. Because this patient population is at particularly high risk for CRC, it is advisable to consider UDCA in all patients with colitis complicated by PSC. For patients without PSC, sufficient data do not exist to recommend it for the purpose of cancer prevention. Five of the six corticosteroid studies have found a beneficial effect of systemic steroids, although most did not reach statistical significance. Regardless, given the frequent and serious adverse effects associated with chronic steroid use, systemic corticosteroids should not be prescribed for this indication. Budesonide, an oral corticosteroid with minimal systemic absorption, is a potential alternative, although it has not yet been studied as a chemopreventative agent. Similarly, until the long-term safety of chronic NSAID use can be demonstrated in patients with IBD, the role of NSAIDs in chemoprevention remains undefined. Although the data are conflicting, immune-modulating medications, such as AZA, do not seem to confer any reduction in the risk of dysplasia or CRC. The data on calcium supplementation and statin use are still too limited to endorse their use for the prevention of colitis-related CRC. Chemoprevention is an area that holds great promise in the reduction of morbidity and mortality associated with IBD. Further studies, including prospective trials when possible and cost-effectiveness analyses, need to be performed to develop an optimal strategy for the reduction of cancer risk in patients with IBD.

Nutritional interventions and outcome in patients with cancer or preinvasive lesions: systematic review

BACKGROUND

Dietary modifications and supplements are used widely by patients with cancer and preinvasive lesions as an adjunct to standard treatment. Given the widespread use of nutritional modifications and supplements by such patients and concerns about the lack of benefit and possible harm, we conducted a systematic review of randomized controlled trials to examine the effect of nutritional interventions on patients with cancer or preinvasive lesions.

METHODS

We searched electronic databases and reference lists to locate all eligible trials and analyzed trial quality. Outcome measures were all-cause and cancer mortality, disease-free survival, cancer recurrence, second primary cancer, recurrence of a preinvasive lesion, or progression to cancer. Results of individual trials were combined by use of random-effects meta-analyses.

RESULTS

We identified 59 eligible trials, 25 in patients with cancer and 34 in patients with preinvasive lesions, respectively. Trial quality was generally low; only three trials (two of cancer and one of preinvasive lesions) had adequate methods for generating the allocation sequence, allocation concealment, and masking both outcome assessors and participants. The combined odds ratio (OR) for the effect of a healthy diet-given alone or with dietary supplements, weight loss, or exercise-on all-cause mortality was 0.90 (95% confidence interval [CI] = 0.46 to 1.77). There was no evidence of an association between the use of antioxidant (OR = 1.01, 95% CI = 0.88 to 1.15) or retinol (OR = 0.97, 95% CI = 0.83 to 1.13) supplements and all-cause mortality. Meta-analyses of all other outcomes did not show clear evidence of benefit or harm.

CONCLUSIONS

The impact of most nutritional interventions cannot be reliably estimated because of the limited number of trials, many of which were of low quality. There is no evidence that dietary modification by cancer patients improves survival and benefits disease prognosis.