As part of the digestive tract, the large intestine consists of the caecum (or cecum), ascending colon, transverse colon, descending colon, sigmoid colon and the rectum. Colorectal cancer refers to a cancer arising from these parts of the large intestine. The anatomy of the large intestine is shown in the picture provided.
Colorectal cancer generally affects older patients with the median age of 67 years old. We do see quite a few younger patients with colon and rectal cancers. The risk of colorectal cancers increases after the age of 50.
Signs and Symptoms :
- Change in bowel habits (constipation, diarrhoea or it could be alternating constipation/diarrhoea)
- Blood in the stools
- Feeling tired or weak (it could be from anaemia)
- Low iron level (iron deficiency anaemia)
- Black or dark-coloured stools
- Stomach pain or frequent colic pain in the abdomen
Risk Factors
- A family history of colorectal cancer (such as familial adenomatous polyposis (FAP), hereditary nonpolyposis colon cancer (HNPCC))
- A diet high in red and /or processed meat and low in fruits and vegetables
- Physical inactivity
- Obesity
- Smoking
- Heavy intake of alcohol
- Certain conditions like inflammatory bowel disease
Screening for Colorectal Cancer
It is possible to detect
colorectal cancer at an early stage before symptoms arise. This is usually done by a faecal or stool occult blood test (FOBT).The other screening modality is
colonoscopy which is used to look inside the rectum and large intestine. It has the advantage of removing precancerous polyps if they are detected. It can often be done as a day procedure. If no abnormal findings are detected, the next
colonoscopy is more than 5 years later. For individuals at increased risk,
colonoscopy is recommended for screening.
The age to start screening is 50 years old for the general population. However, depending on
risk levels such as having a parent or sibling with
colon or rectum cancer, or the presence of specific hereditary genetic syndromes, your doctor may recommend an earlier age for screening after assessment of cancer risk.
Staging for Colon Cancer
Once a diagnosis of colorectal cancer is made, staging is the next process to determine the extent, aggressiveness and spread of the cancer so that appropriate treatment can be planned. The staging evaluation, tests and investigations for a newly diagnosed colorectal cancer include:
- Physical examination
- CT scan or MRI of the abdomen and pelvis
- Chest X-ray
- Histopathology – how the cancer looks like when viewed under the microscope, after it has been removed at surgery.
- Specific mutations related to colorectal cancer as needed such as KRAS, NRAS, BRAF.
Colorectal cancer stages range from stage 1 to stage 4.
In stage 1 colorectal cancer, the
cancer has invaded into but not through the entire wall of the intestine. It has not spread to nearby lymph nodes or distant sites.
The stages 2 and 3 refer to further localised invasion which may or may not have regional lymph node involvement.
Stage 4
colorectal cancer is when the cancer has spread to distant organs, such as the liver or lungs.
Treatment depends on the disease stage. Localized colorectal cancers are generally treated with surgery, with or without chemotherapy and radiotherapy. The drugs used are 5
fluorouracil (5FU), oxaliplatin, leucovorin (folinic acid) and capecitabine (Xeloda). Advanced (stage 4) colorectal cancer is generally treated with chemotherapy and targeted therapy. Occasionally, some patients may benefit from surgery of the primary tumor and sometimes of metastases.
