Exploring the connection between colorectal cancers and genetics, diet and lifestyle

Colon cancer, rectal cancer, colorectal cancer, or bowel cancer. The name changes depending on where the malignancy originates, but diagnosis, genetics and management has become more uniform and standardised. A leading medical oncologist takes a look at this important talking point in this informative article. 

How do genetics affect the risk of developing colorectal cancer?

A lot about the genetics of colorectal cancer is yet to be discovered. We know that 100 per cent of patients with hereditary mutations of the APC gene develop colon cancer by 40 years of age. We know HNPCC (hereditary nonpolyposis colon cancer syndrome, also known as Lynch syndrome) has a 40 per cent risk of colorectal cancer, as well an increased risk of developing urothelial cancer, endometrial cancer or other cancers.

It’s also been found that deficient mismatch repair (dMMR) and possibly other undiscovered genes are highly prevalent in colon cancer (particularly Lynch syndrome).

How does diet have an effect?

It’s thought that low fibre diets, high in red meat and animal fat (Tabung et al.), and those low in fruit/vegetable intake increase the risk of colorectal cancer. One study (Aune et al.) found high fibre diets that contain cereal fibre and whole grains reduced the risk of this type of cancer; while a study by Pala et al. argued that yoghurt intake also decreased risk of the disease.

Risk is high in overweight men, yet also in lean women (Jacobs et al.), with WNT-CTNNB1 gene. Men or women who drink alcohol (Cho et al.), and patients with history of inflammatory diseases (Crohn’s disease, ulcerative colitis) are also associated with high risk.

How common is colorectal cancer?

Rates of colorectal cancer and rates of mortality have actually gone down for many decades. From 2007 to 2016, incidence has decreased by 2.4 per cent annually. However, according to leading charity Cancer Research UK, these types of cancers are the fourth most common cancer in the country.

What other factors add to the risk of developing colorectal cancer?

There are now a number of key factors that predict outcomes for colorectal cancer patients:

• If the size is greater than five centimetres,
• If there is disease-free interval of less than a year.
• If there is more than one tumour.
• If the primary lymph-node is positive for cancer
• If the patient’s antigen (Aggarwal et al), and or t-cells levels are high (Katz et al).
• Patients with pre-existing mental disorders.
• Patients that have not had aspirin, which is a well-known ameliorator of colon cancer (Rothwell et al; Burn et al)
• Patients that have not had surgery, chemotherapy or radiation therapy.
• Patients that smoke
• Patients with diabetes mellitus or cardiovascular disease risks (Dehal et al).

What are the symptoms of colorectal cancer?

Common symptoms of colorectal cancer include:

• Abdominal pain
• Iron-deficiency anemia
• Rectal bleeding
• Change in bowel habits
• Intestinal obstruction/perforation

Right-sided lesions (associated with younger age), have the following common symptoms:

• Bleeding
• Diarrhea

Left-sided tumours (associated with older age), have the following major symptom:

• Bowel obstruction

Can colorectal cancer be mistaken for anything else?

Care must be made to ensure colon cancer is being treated, and not similar diseases, for example:

• Carcinoid/neuroendocrine tumors and rare tumors of the GI tract
• Ischemic bowel
• GI lymphoma
• Small intestine carcinoma
• Arteriovenous malformation (AVM)

Particular emphasis must be made to distinguish between colon cancer and:

• Crohn’s disease
• Ileus
• Small intestinal diverticulosis
• Ulcerative colitis