HEQ examines risk factors and screening protocols for the world’s third most common form of cancer – colorectal cancer.
With more than 1.8 million new cases reported in 2018 – a 9.5% increase compared to 1990 – colorectal cancer is the world’s third most prevalent form of cancer: the second most common cancer type in women and the third most common for men.
Evidence gathered by the World Cancer Research Fund indicated that diet and lifestyle have been key contributing factors in the rise in incident cases of colorectal cancer, with excess body weight, consumption of processed meat, and drinking alcohol all reported to increase the risk of contracting the disease.
Incidence and spread of colorectal cancer
The majority of colorectal cancer cases begin with the appearance of polyps on the inner lining of the rectum or colon: adenomatous polyps can be a pre-cancerous condition, while hyperplastic and inflammatory polyps rarely become cancerous.
Significant risk factors in the incidence of colorectal cancer include:
- Family history of colorectal cancer
- Excess weight and obesity
- Diet, particularly lowered consumption of calcium or fibre
- A sedentary lifestyle
- Alcohol consumption
Adenocarcinomas, which begin in the glandular cells which produce the body’s mucus, make up around 96% of all cases of colorectal cancer – the remaining 4% comprises carcinoid and gastrointestinal stromal tumours, sarcomas, and lymphomas. If an adenomatous polyp is not removed, it may spread from the mucosa layer of the colon or rectal wall; once a cancerous growth has spread to the outer wall of the colon or rectum, it can then spread further into the lymph nodes through blood vessels and lymph vessels.
Symptoms and diagnosis
In its earliest stages, colorectal cancer is commonly asymptomatic. Once symptoms do begin to present, the most common signs of colorectal cancer include blood in the stool; abdominal pain and discomfort; and persistent changes to the bowel habits. In the UK, pre-emptive screening for colon cancer is offered to patients aged 55 or over; with patients aged over 60 invited to complete a home test every two years. Initial screenings for colorectal cancer commonly consist of either faecal immunochemical tests (FIT), where faecal samples provided by the patient are analysed for traces of blood, or flexible sigmoidoscopies, which have been introduced more recently and which checks the colon for polyps using a camera. Patients whose FITs and sigmoidoscopy tests exhibit abnormalities may then be referred for a secondary colonoscopy screening.
Researchers and oncologists have expressed concern over the risk of false positives arising from faecal testing: false positives occur in around 25% of tests; and are usually incurred by the presence of blood in the stool from issues such as inflammation or haemorrhoids. The rate of false positive FIT results increases the burden on health providers of unnecessary colonoscopies, leading to financial and time costs for hospitals and unwarranted stress for patients. A 2013 study published in the International Journal of Cancer under the title ‘Risk factors for false positive and for false negative test results in screening with faecal occult blood testing’ highlighted the additional risk that false positive results may lead to reluctance on the part of patients to undergo further testing, saying: ‘A false positive test result will lead to unnecessary colonoscopies, accompanied by extra costs, burden and risks for the patient, which could affect participation in screening programmes. It has been shown that women with a false positive mammography were less likely to attend to subsequent screening rounds. Also, being recalled for further diagnostic tests can evoke high levels of (in the case of a false positive test, unnecessary) anxiety and a lower quality of life.’
While confirmed diagnoses of colorectal cancer have risen significantly in real terms in the last 30 years, deaths associated with colorectal cancer have fallen by 13.5% in the same period. This is largely attributable to greater uptake of early screening on the part of patients; a 2015 study conducted by Dr Ann G Zauber of Memorial Sloan Kettering Cancer Center, New York, and published in the Digestive Diseases and Sciences journal, found that: ‘[M]ore than 50% of the decline in colorectal cancer mortality can be attributed to the increased acceptance and uptake in colorectal cancer screening. Current and future levels of increased screening could provide for even larger reductions for the US. Colorectal cancer screening has, and will, continue to make a significant impact on reducing colorectal cancer mortality.’
Treating colorectal cancer
In cases where colorectal cancer has been detected early, surgery to remove cancerous polyps can have a high success rate in treating and arresting the spread of cancer. In the
later stages, chemotherapy, radiotherapy, immunotherapy or biological treatments may be indicated. Approximately 5% of colorectal cancer cases occur in patients with hereditary Lynch syndrome, which heightens the risk of contracting certain cancer types; the tumours which occur as a result of Lynch syndrome have a higher than average number of mutations, meaning that patients with Lynch syndrome are particularly receptive to immunotherapy drugs.
A research programme, led by Dr Steven Lipkin of Weill Cornell Medical College in New York, is working on the development of a vaccine to protect patients with Lynch syndrome against the appearance of cancerous tumours. The programme has so far shown positive results in trials of a vaccine on mice with Lynch syndrome, though trials on human subjects may take several more years to complete. Dr Louis M Weiner, Director of Washington DC’s Georgetown Lombardi Comprehensive Cancer Center, said: “The holy grail is a cure [for cancer] – a holier grail is prevention.”
This article is from issue 14 of Health Europa. Click here to get your free subscription today.