Appropriate treatment of colorectal cancer depends on:
- Patient fitness and preference
- Location of cancer
- Stage of cancer
- Extent of distant spread
Colorectal cancer refers to cancer that starts in the colon or rectum. Cancer occurs when there is an uncontrolled growth of cells. Typically, colorectal cancers begin from benign growths (polyps) on the inner lining of colon or rectum. Not all polyps will turn into cancer, but adenomatous (cancers that begin in cells that produce mucus and other fluids) polyps may have the potential to grow into colorectal cancer after many years.
More than 95% of colorectal cancers are adenocarcinomas. Very rarely, cancers of colon and rectum are due to carcinoid tumours, gastrointestinal stromal tumours (GIST), lymphomas or sarcomas. This writeup refers to colorectal adenocarcinomas.
Colorectal cancer is very prevalent in Singaporeans. In fact, it is the most common cancer in Singaporean men and the 2nd most common cancer in Singaporean women1. Furthemore, Singaporean men have the highest incidence of colorectal cancers within Southeast Asia, with incidence rates as high as western countries2.
Every day, 3 Singaporean men and 2 Singaporean women are diagnosed with colorectal cancers1. Of great concern is the increase in the global incidence trend of colorectal cancers in adults younger than 50 years old. The National Cancer Institute’s SEER Registry (USA) showed the incidence of colorectal cancer is increasing at 2% per year3. More than two-thirds of colorectal cancers in younger adults are not associated with a family history of colorectal cancers and tend to be diagnosed at later stages while requiring a more aggressive clinical course.
In general, colorectal cancers begin when healthy cells in the colon develop changes (mutations) in their DNA. Usually, many changes in DNA over time are required to cause cells to grow out of control.
Most of these DNA changes are sporadic and poorly understood. Certain modifiable risk factors increase the chance of acquiring these DNA changes. They include:
There are risk factors that cannot be controlled including:
Colorectal cancers may present with:
However, most early-stage colorectal cancers generally have little to no symptoms when the growth is small. Hence, screening for polyps and cancers remains the single most effective strategy in decreasing the mortality from colorectal cancers.
Screening for colorectal cancer means testing healthy, at-risk people, who have no symptoms. The idea is to identify polyps and cancer at the early stage so that intervention bears the highest chance of cure. Unfortunately, in Singapore, only about 2 in 5 individuals who are 50 to 69 years of age go for colorectal cancer screening at the recommended frequency.
There are various screening methods developed for colorectal cancer, with each test having its own pros and cons.
Colorectal cancers are diagnosed formally by colonoscopy and biopsy of any suspicious mass seen. Occasionally, patients present with stage 4 disease and have other accessible sites that are amenable to biopsy under radiological guidance without needing to undergo bowel preparation.
Once the diagnosis of colorectal cancer is confirmed, staging tests will need to be done to determine the stage of cancer and an appropriate treatment plan. Commonly, patients will be asked to undergo some basic blood tests and additional scans.
For rectal cancer, MRI rectum will be helpful to determine the extent of local structures / lymph nodes involvement. CT scan or PET scan will be helpful to exclude distant spread of the cancer.
Appropriate treatment of colorectal cancer depends on:
Stage 1 colorectal cancers are generally treated with surgery alone. Some stage 2 colon cancer with adverse features on surgical specimens may require chemotherapy after surgery (adjuvant chemotherapy) to reduce the risk of relapse. Patients with stage 3 colon cancers are generally advised to undergo adjuvant chemotherapy after surgery. Stage 4 colon cancers are generally treated with chemotherapy, targeted therapies or immunotherapy. Select patients with stage 4 colon cancer who have limited spread, especially in the liver or lungs, may be suitable for curative intent surgery /local ablation plus chemotherapy. Radiotherapy has a well-defined role prior to surgery in locally advanced rectal cancer, to improve local control and reduce local recurrence. It can also be used to ablate limited sites of metastatic disease.
Radiation therapy is the use of high energy rays to destroy cancer cells. Radiotherapy may be used in the following circumstances:
Locally advanced rectal cancer that is being considered for surgery may benefit from upfront radiotherapy (usually in combination with chemotherapy) prior to surgery to reduce local recurrence rate. Delivery of radiotherapy treatment prior to surgery is better tolerated than radiotherapy after surgery and associated with no increase in surgical complications.
May help to improve symptoms such as pain / bleeding from bulky cancer pressing on vital structures.
Immunotherapy involves the administration of intravenous antibodies to boost immune recognition and killing of cancer cells. Approximately 3-5% of patients with inoperable stage 4 colon cancer have a deficiency in DNA mismatch repair (dMMR). Based on recent data from Keynote-177 trial, single agent Pembrolizumab is superior to first line chemotherapy with fewer side effects and much more durable response8. Immunotherapy may also be beneficial in patients with high tumour mutation burden (TMB) as defined by next-generation sequencing of tumour tissues.
Colorectal cancer is a common cancer in Singaporean men and women. There is also a rising trend for a younger age of onset. Appropriate screening tests aim to identify precancerous polyps and early stage colorectal cancers, with the goal of increasing the chances of long-term cure. There have been major advancements in the treatment of colorectal cancer with better treatment selection tools, better chemotherapy and targeted therapy, more modern surgical and radiotherapy techniques and better supportive care. Consult our oncologists for colorectal cancer treatment in Singapore.