Chapter 24 Large bowel cancer

Introduction

Bowel cancer screening

Colorectal cancer (CRC) is one of the most common forms of cancers in the Western world. Lifetime risk to age 75 in the general population is 1:17 for men and 1:26 for women in Australia and is the second leading cause of death.¹

Research shows that the risk of developing bowel cancer rises significantly from the age of 50 and accounts for 85% of sporadic cancers.²

Most cancers of the bowel arise from polyps (adenomas) and removal of polyps markedly reduces the subsequent risk of disease.³

Various countries are in the process of introducing national screening programs, and in Australia a population of greater risk are invited to take part in the program.¹

The eligible population in Australia is those turning 50, 55 and 65 years of age between January 2008 and 31 December 2010. In the US, screening will commence at a similar age (50).⁴ People eligible to participate in the program will receive an invitation through the mail to complete a faecal occult blood test (FOBT) and no cost is involved. There is controversy as to which is the best screening method and also which is the best FOBT.^2,^5,⁶ In the US, FOBT will also be used.

There is also increasing evidence to support the use of virtual colonoscopy as an initial screening test.⁷

If the FOBT is positive, the participant will be advised to discuss the result with their doctor who will generally refer them for a colonoscopy.⁴ Doing an FOBT every 2 years can reduce the risk of dying from bowel cancer by up to one-third.²

High-risk patients such as those with familial adenomatous polyposis and hereditary non-polyposis CRC need to be screened more frequently. As with all other screening tests, there needs to be an emphasis on combining screening with prevention, in particular with CRC where there is considerable research data on prevention.⁸

Lifestyle and prevention

The importance of prevention has been highlighted by Baker and Wardle, even suggesting that lifestyle changes could prevent more colorectal than screening.⁸ Key lifestyle and dietary factors for primary prevention are:

• behavioural factors

Behavioural factors

Personality factors, especially emotional suppression and loss (and a feeling of hopelessness), have been linked to the occurrence and progression of cancer. Hence, as with almost all chronic illness, behavioural factors have been reported to be important in CRC.^9,¹⁰

Recently a population-based prospective cohort study from Denmark investigated associations between personality traits and cancer survival.¹¹ This study showed that neuroticism was negatively associated with cancer survival. A further recent study reported that certain personality factors may not be a risk factor for CRC in the Japanese population. However the report concluded that an ambivalent connection and egocentricity may be protective.¹²

The relationship between personality traits and cancer remains contentious. However, it should also be noted that behavioural factors play a key factor in influencing other risk factors such as disregard for prudent eating and physical activity regimens which may increase the risk for the development of large bowel cancer.

Physical activity/exercise

Regular and vigorous physical exercise has been scientifically established as being a strong preventative factor against cancer with the potential to reduce incidence by 40%.¹³ With respect to bowel cancer, physical activity can decrease its incidence by 50%, independent of diet and body weight.¹⁴

Mind-body medicine

The diagnosis of cancer presents a major and stressful life event that necessitates an adaptive adjustment to sustain quality of life. A fundamental goal is to enhance quality of life while striving to prolong life. Quality of life has been reported to predict survival in patients with advanced large bowel cancer.¹⁵

Surveys of patients with cancer repeatedly identify information provision as a major unmet need. Research has shown that the provision of adequate information is related to an increase in psychological wellbeing.¹⁶ Effective communication skills ensure that this information is clearly explained and understood.

There is incontrovertible evidence from 3 meta-analysis of the benefits of psychological interventions in patients with cancer. Such interventions improve emotional adjustment (including anxiety and depression, sense of control, self-esteem), functional status (including daily living activities, social and disease-related symptoms (e.g. like nausea. vomiting, pain) and overall quality of life.^17,^{18, 19}

There are wide benefits from relaxation-based therapies in reducing anxiety, treatment-related phobias, conditioned nausea and vomiting and insomnias.¹³

Both cognitive behavioural therapy (CBT) and supportive expressive therapy are effective in countering existential fears of dying, aloneness, meaninglessness, and unrealistic fears about the processes of treatment.¹³^–¹⁶

Nutritional influences

Diet

Excess energy intake/fat and carbohydrates

Execss energy intake has been shown to be consistently associated with bowel cancer.²⁰

Fat intake is closely associated with energy intake, it has been difficult to differentiate between the two, to add to this confusion a meta-analysis found little evidence of any energy-independent effect of either total or saturated fat.²¹

Several prospective, observational studies have shown that diet is a major factor in the aetiology of large bowel cancer, with high fish consumption highlighted as decreasing CRC risk. A problem with most of the older studies has been that fats, such as those from fish fats which have been shown to be protective in more recent studies, were not differentiated from other fats.^22,²³

A recent randomised clinical trial (RCT) objectively investigated the effects of a 6-month intervention with oil-rich or lean fish versus dietary advice only, on apoptosis and mitosis within the colonic crypt. The participants had either colorectal polyps, inactive ulcerative colitis, or no macroscopic signs of disease.²⁴ The results of the trial showed that the total number of mitotic cells per crypt decreased non-significantly in the salmon group and in the cod group compared with the dietary-advice-only group. The study concluded that an increase in the consumption of either oil-rich or lean fish to 2 portions weekly over 6-months did not markedly change apoptotic and mitotic rates in the colonic mucosa. Moreover it should be noted that fish fats consumption may be a lifetime strategy, not just a short-term solution. A recent review unequivocally concludes that intake of fish fats has a favourable effect on lowering cancer risk.²⁵

High consumption of trans-fatty acids is linked to colorectal adenomas.²⁶

There is confusion as to whether carbohydrate intake can influence CRC, but it would be very unlikely that refined carbohydrates were not a risk factor.^27,²⁸

Meat

A meta-analysis of studies on meat and CRC risk showed that it is a risk factor. Much of the risk was associated with processed meat.²⁹

Dietary fibre

An inverse correlation between plant food and intake in cancer risk in 8 of 10 case-controller cohort studies has been published.³⁰

A systematic review of case-control studies found that 12 out of 13 showed a decreased risk of CRC with increased fibre intake.³¹

A huge and more recent study of 519 978 participants also showed that fibre intake reduced risk.³²

Vegetables and fruit

Vegetables and fruit are more consistently protective against CRC than cereals in case-control cohort studies.²⁵ It is unknown whether vegetable or fruit offer most protection. In general, cruciferous vegetables appear to offer special protection.³³

It is likely that the non-fibre vegetable components such as phytonutrients, and vitamins and minerals offer special protection.

Resistance starch

Resistance starch includes those carbohydrates that escape digestion in the small intestine.³⁴

Resistance starch produces the highest level of faecal butyrate which is protective against large bowel polyp/cancer formation.³⁵

Nutritional supplements

Micronutrients

Probiotics/prebiotics

Probiotics and prebiotics are likely to be protective, in particular as they greatly influence the internal bowel environment.⁴⁸

A number of studies demonstrate that probiotics alter bowel microflora and decrease premalignant and malignant lesions in laboratory experiments in animal studies.^49,⁵⁰

Radiation enteritis is a severe problem in patients receiving irradiation of the abdomen or pelvis in the course of cancer treatment. Experimental studies in animal models and clinical trials of patients with inflammatory bowel disease (IBD) have consistently shown that the use of probiotic organisms may effectively down-modulate the severity of intestinal inflammation by altering the composition and metabolic and functional properties of indigenous flora of the gut.⁵¹ Recently a multi-centre randomised study demonstrated that nutritional intervention with the probiotic drink containing L. casei DN-114 001 does not reduce the incidence of radiation-induced diarrhoea as defined by a Common Toxicity Criteria Grade 2 or greater. However, it had a significant effect on stool consistency as measured by the Bristol scale.⁵² However an earlier study with 490 patients who underwent adjuvant postoperative radiation therapy after surgery for sigmoid, rectal, or cervical cancer and who were assigned to either the high-potency probiotic preparation VSL#3 (one sachet 3 times a day [tid]) or placebo starting from the first day of radiation therapy showed that with a multi-strain preparation it protected cancer patients against the risk of radiation-induced diarrhoea.⁵³