Colorectal Cancer Risk Factors and Prevention

Colorectal Cancer

Colorectal cancer (CRC) is considered as the growth of cancerous cells originating in the colorectal region. The primary cause of CRC is a precancerous polyp. If left untreated can lead to cancer originating in the large intestine or rectum area^(1).Prevention efforts have been introduced worldwide and in New Zealand (NZ), which have seen incidence and mortality rates stabilise and decrease over time⁽²⁾. Globally however developing countries incidence however are still rising while developed countries have either stabilised or decreased. The continuous decline in death rates from all cancers together for both male and female reveals the influence of increased screening, decline in risk factors and enhanced treatment ⁽³⁾. Therefore, CRC development can be prevented and reduced with the appropriate screening program, and many still remain affected by the disease then prospects of control are of worldwide public health importance.

 CRC effects a large variety of the global population, therefore primary, secondary and tertiary levels on prevention must be considered. The primary interventions discussed in this report will target the modifiable risk factors, while the secondary prevention will focus on screening allowing for early detection for reduce the burden.

Colorectal cancer is a key cause of cancer mortality and is considered to be largely attributed to lifestyle factors and behaviour patterns⁽⁴⁾. Data suggests that lifestyle risk factors comprising of diet, physical activity, obesity and diabetes have a pivotal role in the aetiology of the disease. Other risk factors determinants include smoking and a history of previous adenomatous polyps. Most of these risk factors are modifiable and therefore preventions can be set in place to reduce risk. However, risk factors such as previous personal or family history of adenomatous polyps are unmodifiable risk factors which still must be addressed when thinking about prospects of control. Both global and national CRC risk increase with age therefore interventions must be aimed to reduce this. Risk factors commonly affect disease development in the long term rather than instant, therefore when looking at reducing the general burden of the disease this should be considered ⁽³⁾.

Obesity, physical inactivity and BMI

Physical inactivity, high body mass index (BMI) and obesity are interrelated risk factor determinants for colorectal cancer. Studies suggest a dose response affect, that reflects the regularity and intensity of physical activity which is inversely related to CRC⁽⁵⁾and studies find as little as 7 hours a week could lower the risk of CRC⁽⁶⁾. These are interrelated risk factors due to the fact that increasing BMI is linked to decrease in physical activity⁽⁷⁾therefore lead to obesity. Risk is believed to increase with increased BMI since there’s an increase in circulating estrogens and decrease in insulin sensitivity, therefore, this is assumed to influence cancer risk⁽⁵⁾. A study uncovered that overweight physically inactive men had a greater risk of colon cancer yet overweight physically active men had a lower risk. These results insinuate that high BMI in active males suggests there is more lean body mass compared with inactive men⁽⁶⁾. The underlying mechanism of attack in colon carcinogenesis are alike for both obesity and high physical inactivity⁽⁸⁾. One of the probable mechanisms underlying the relationship is that persistent physical activity causes a rise in digestion in the body, increasing gut motility and maximal oxygen uptake, long term this increases the metabolism efficiency and a lower blood pressure and insulin resistance⁽⁵⁾.

Diet

The percentage of CRC accredited to nutritional elements has been predicted to be 50%, approximately a further 66-77% of CRC is believed to be avoidable by an appropriate combination of nutrition and lifestyle modifications ⁽⁴⁾. CRC is increasingly more common in high income countries and believed to be linked to the westernised diet⁽⁹⁾. A standard western diet is defined as energy dense and contains large consumptions of red and processed meat, refined grains, carbs and sugar containing foods; less fruit and vegetables⁽⁵⁾. Consumption of red meat shows an inclined risk but other protein rich sources do not have this effect and many reduce the incidence of colon cancer⁽⁶⁾. It is believed that meat consumption is more connected to colon cancer rather than rectal⁽⁹⁾. The primary potential mechanisms for this link is due to the produced carcinogens produced when red meat is cooked⁽⁵⁾. There is an inverse link amongst ingestion of fruits and vegetables and risk witnessed in various case control studies⁽⁶⁾. A large intake of fruits and vegetables, having dietary fibre, dilute faecal content, increase faecal bulk reducing transit time which reduces risk⁽⁵⁾. Sections in Africa had low rates of CRC where intake levels of fibre is elevated initially led to the theory that high fibre lowers the risk of colon cancer⁽⁶⁾.

Smoking

Smoking is damaging to the colorectal region due to the carcinogens in tobacco which promotes cancer growth, as well as incidence and mortality rates⁽⁹⁾. A metanalysis conducted shows current smokers have a much higher risk of developing polyps than non-smokers, as well as a larger risk of recurring adenomas than non-smokers⁽⁵⁾. Another study also found that long term smoking over 3-4 decades is a main risk factor for colorectal cancer. Evidence is consistent with the idea that smoking promotes the growth of adenomatous polyps, especially more violent adenomas⁽³⁾. The risk rates vary for smoking due to the variation of duration, cigarette type and the amount of cigarettes smoked⁽⁴⁾.

Alcohol consumption

Alcohol consumption is a known risk factor determinant for the onset on colorectal cancer at a young age⁽⁹⁾. Increased alcohol consumption leads to increase CRC risk. Alcohol intake is related to higher risk of colorectal adenoma, which consequently provides an increased risk⁽⁶⁾. Acetaldehyde is believed to also carcinogenic⁽⁹⁾. Alcohol also functions as a solvent, resulting in the increased infiltration of other carcinogenic molecules in mucosal cells⁽⁵⁾. Alcohol when combined with an unhealthy diet is believed to be exceptionally strong by effecting metabolism rates⁽⁶⁾ and in turn making tissues susceptible to carcinogenesis⁽⁵⁾. A study found those in the highest group of alcohol consumption had approximately 60% greater risk⁽⁴⁾. A dose response between risk of colorectal cancer and consumption. International correlation studies show a strong association between the consumption of beer and rectal cancer⁽⁸⁾. In New Zealand, also international correlation studies conducted found beer consumption contributed to the high colorectal mortality⁽¹⁰⁾.

History of adenomatous polyps

CRC generally begins with an adenomatous polyp. The lifetime risk of developing a colorectal adenoma in the US population is almost 19%, and an estimated 95% of CRC’s develop from these⁽⁹⁾. If left untreated the polyp may become cancerous leading to cancer. The risk is increased among people with a strong family history, like a history of CRC or adenomatous polyps in a first degree under 60 years⁽⁵⁾. People with a personal history of developing adenomatous polyps have a higher risk of growth, the discovery and removal of an adenoma before the malignant change can lower the risk of CRC although complete removal may increase the chances of future development of metachronous cancer elsewhere in the colon and rectum⁽⁹⁾. Malignancy rates are believed to be higher for those with adenomas larger than 1cm⁽⁵⁾.

Primary preventions

Colorectal cancer is a prominent factor of cancer mortality and is considered to be mainly attributed to lifestyle and behavioural patterns⁽⁴⁾. Many cancers have modifiable risk factors, but improvements due to risk factor modifications are seen over a long period of time⁽³⁾. Therefore, the best way to reduce colorectal incidence is to educate and offer awareness to the community, which is best done through campaigns. Providing young adults with the education and awareness allows people to make educated lifestyle modifications and provides awareness on the importance of adherence to screening guidelines in the future ⁽¹¹⁾.

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The Never Too Young campaign has been organised by Bowel Cancer New Zealand (BCNZ), is a nationwide campaign to raise the awareness to bowel cancer⁽¹²⁾. BCNZ is a national charity which raises aware ness of bowel cancer, supporting patients and providing education to the community⁽¹²⁾. Move your Butt is another campaign which is held through the month of June, which urges people to challenge themselves and exercise more than they regularly do⁽¹³⁾. In the United States, the Don’t Assume campaign uses the month of March to provide public awareness. The objective is to challenge assumptions and misconceptions about CRC, and raising awareness while providing information and support⁽¹⁴⁾.

Secondary prevention

Screening is the dominant strategy used to address colorectal cancer through secondary prevention⁽¹¹⁾. The main screening tests used worldwide is Faecal Occult Blood Test (FOBT), sigmoidoscopy and colonoscopy. A FOBT is a test which look for early signs of bowel cancer, by looking for blood⁽¹⁵⁾, a study discovered that when tested annually reduced mortality by 33%⁽¹⁶⁾. A colonoscopy, examines the mucous of the surface of the whole colon, while a sigmoidoscopy allows the examination of the mucous surface of the lower colon only ⁽¹⁶⁾. A study found sigmoidoscopy reduced incidence or mortality by 60% and a colonoscopy reduce incidence by 75%. New Zealand has made the recent decision to proceed with a national population based biennial faecal immunochemical test (FIT) based program. Which is consistent with international evidence⁽¹⁷⁾.

National Bowel Screening Programme (NBSP) is a free screening programme for New Zealanders aged 60-74 years with the goal to reduce incidence and mortality through early detection⁽¹⁸⁾. The programme allows all New Zealanders regardless of ethnicity or community the opportunity be screened⁽¹⁸⁾. The purpose of this is to detect adenomatous polyps, before a malignant stage or as early as possible allowing for the best chance of survival. A bowel screening programme found 5 in 10 people who has a colonoscopy has adenomas detected and 4 in 100 people who has a colonoscopy after their first screening were found to have CRC and referred for treatment⁽¹⁹⁾.

Colorectal cancer is a disease with chances for prevention, early detection through improved frequent national screening rates is important but should not be the only strategy to decline the burden. Public awareness and education with screening is believed to be the best approach to reduce incidence and mortality⁽¹¹⁾. Recently there has been a decrease in cases of CRC in the US and a reduction in mortality there and in some European countries. This has been accredited to the effects of changing lifestyle, prompt diagnosis, screening and enhanced therapy⁽²⁰⁾. Since risk factors affect the disease development over the long term, the decrease in incidence and mortality may reflect the primary prevention strategies introduced decades earlier⁽³⁾.

Conclusion

The incidence and of CRC continue to be a public health concern worldwide. Both primary and secondary prevention processes have been put in place to target the burden of CRC. With a focus on lifestyle alterations; diet, physical activity and obesity, smoking and alcohol intake. decrease risk factors and early detection together are the best approach to reducing incidence and mortality. CRC incidence and mortality rates continue to remain high despite the reduced rates in both New Zealand and globally. Consequently, the need for ongoing research into improved CRC interventions are still required.

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