Colorectal cancer originates in the colon or rectum, the terminal end of the digestive tract. The secular trend of colorectal cancer has been increasing in developing countries globally, including Thailand. It is the third most common cancer worldwide. According to the World Health Organisation (WHO), there are about 1.9 million newly diagnosed colorectal cancer cases annually, with over 900,000 deaths in 2020. In Thailand, colorectal cancer is the most common cancer in men, accounting for 20.7%, and the second most common cancer in women, accounting for 12.2% of all cancers diagnosed in 2020.
Colorectal cancer can affect anyone, but certain factors can increase an individual's risk. Advancing age is one of the significant risk factors for colorectal cancer, increasing as people get older, particularly over 50. African Americans carry a higher individual risk of developing colorectal cancer than other ethnic groups. Other risk factors for colorectal cancer include a family history of colorectal cancer or polyps, a history of certain colorectal diseases, particularly inflammatory bowel disease (IBD; Crohn's and ulcerative colitis), and some genetic syndromes. Modifiable factors that can increase the risk of developing colorectal cancer include smoking, alcohol consumption, unhealthy diets such as those high in red and processed meat, and a lack of physical activity.
When abnormal cells in the large intestine divide uncontrollably, it begins to form a small polyp, a benign but precancerous lesion, which can potentially grow into a large mass and eventually transform into invasive cancer if left untreated. This premalignant phase may last a few years, allowing a window of opportunity to nip cancer in the bud. The symptoms of colorectal cancer vary by the stage and location of the tumour. In the early stages of a polyp, it may be asymptomatic. In the later stages, as a large tumour, it crowds out the colonic lumen causing the patient to have changes in bowel habits such as diarrhoea, constipation, or smaller stool calibre, which may portend future colonic obstruction. Other symptoms include abdominal pain, blood in the stool, weakness or fatigue from anaemia, or unexplained weight loss.
Colorectal cancer diagnosis relies on a combination of history, physical examination, and tissue diagnosis. Colonoscopy is the examination of the colonic lumen using a long, flexible endoscope with a lens and fibreoptic light source at the tip inserted into the rectum and passing through the colon. Excision of a whole polyp or tissue biopsy from a large tumour through a colonoscope is routinely feasible. Doctors may order investigations such as tests for tumour markers or imaging studies to corroborate the cancer diagnosis.
Unfortunately, most colorectal cancer patients are diagnosed when the tumour has grown to be large and symptomatic. With a late diagnosis, the prognosis of the disease is worse, requiring more complex treatments. In contrast, early detection of small or precancerous lesions is crucial for favourable treatment outcomes. Therefore, everyone at risk should have screening for colorectal cancer at the appropriate time.
The American Cancer Society recommends that individuals at average risk of colorectal cancer begin screening at age 45. Individuals at higher risk, such as those with a family history of colorectal cancer or polyps, may need to start screening earlier. Especially for first-degree relatives of a person having colorectal cancer at a younger age, the screening should begin ten years earlier than the age of diagnosis.
There are several approaches to screening for colorectal cancer, including;
- Colonoscopy every ten years: This is the ideal tool for screening colorectal cancer, as it can detect the lesions and remove the precancerous polyp in the same session. Also, doctors can perform a tissue biopsy if they find a large tumour. Repeat the screening colonoscopy in ten years if the examination is normal.
- Faecal immunochemical test (FIT) annually: To detect occult blood in the stool, which may indicate the presence of a polyp or cancer in the colon. If the FIT test is positive, a colonoscopy is required.
- Stool DNA test every three years: To check for mutated DNA in your stool, which may indicate, as in the FIT test, an abnormal lesion in the colon. A positive stool DNA test requires further colonoscopy.
- CT colonoscopy every five years: Using the CT scanner to acquire and reconstruct 3D images of the colonic luminal surface as a virtual colonoscopy for polyp and cancer detection. However, any abnormal lesion detected requires a colonoscopy to remove the polyps or obtain a tissue diagnosis.
- Flexible sigmoidoscopy every 5–10 years: Utilising a shorter flexible scope to examine the left side of the colon, this is a limited version of colonoscopy that does not require whole bowel cleansing before the procedure. However, if the imaging study shows a polyp, further bowel preparation for a formal colonoscopy is recommended.
Selecting a screening method depends on your preference, either for a less invasive two-step screening test or to proceed directly to the one-step screening colonoscopy.
After a diagnosis of colorectal cancer, the treatment plan is determined according to the stage of the disease. In the early stage, when cancer is non-invasive, only endoscopic polypectomy may be sufficient for definite treatment. The later stage of colorectal cancer usually requires surgical resection to remove cancer or prevent tumour complications, especially obstruction of the colon. Currently, minimally invasive, or laparoscopic, surgery is considered the best option due to its smaller abdominal wounds and shorter recovery time. The adjunctive treatment for colorectal cancer includes the following:
- Chemotherapy: Using a special class of drugs to eliminate fast-growing cancer cells
- Radiation: Using high-energy X-rays to kill cancer cells
- Targeted therapy: detect specific changes and block the specific points in the cancer's cellular pathways to inhibit abnormal cell growth and prevent cancer from spreading. Sometimes, checking for specific gene mutations is necessary before selecting a targeted therapy.
- Immunotherapy: Aim to trigger the host body’s immune system to attack and kill the cancer cells, which sometimes make specific proteins called "checkpoints" to hide from our body’s immune system. For immunotherapy to be effective, specific gene mutations should exist.
The option, sequence, selection, and combination of primary and adjunctive treatment depend on the disease stage, the patient’s condition, and the positivity of a specific, targeted gene mutation.
In conclusion, colorectal cancer is a significant health problem worldwide and is usually detected at a late stage of the disease. Colorectal cancer is preventable through regular screening, which can detect the disease early and lead to favourable treatment outcomes. If you are over 45 or have other risk factors for colorectal cancer, a screening test for the cancer is recommended. And if you experience any suspicious symptoms of colorectal cancer, don't hesitate to seek medical attention. By raising awareness about colorectal cancer and the importance of screening, we can together prevent this disease and save lives.
Author: Dr. Santi Kulpatcharapong, MD. MSc., Gastroenterologist specialising in Gastrointestinal Endoscopy. Gastrointestinal and Liver Centre, MedPark Hospital. Tel +66 2023 3333.
Series Editor: Katalya Bruton, Healthcare Content Editor and Director, Dataconsult Ltd. Dataconsult’s Thailand Regional Forum at Sasin provides seminars and extensive documentation to update business on future trends in Thailand and the Mekong Region. Contact details: info@dataconsult.co.th, Tel: 662-233-5606/7
