In the past 20 years, the incidence of colorectal cancer in Hong Kong is increasing. According to the cancer statistics released by the Hospital Authority, in year 1986, there were 1832 new cases; the prevalence was 33.2 per one hundred thousand populations. However, in year 2008, the prevalence raise to 57.8 per one hundred thousand populations, there were 4,031 new cases. The incidence of colorectal cancer is rising rapidly and now ranks the second in the top ten cancers list. The median age of the patients is 55 years but recently younger patients are affected too.

Etiology

When the growth of normal mucosa cells of the bowel becomes uncontrolled and bizarre, "overgrowth" of the cells happens and form polypoid lesions. This event happens as a result of multiple gene mutations, the polyps can even turn into cancers after 5-10 years of time. Apart from genetic factors, other factors may promote the malignant growth; these factors include cigarette smoking, radiation therapy, high fat and low fiber diet.

Common Symptoms

As the colon is long and occupies different positions in the abdomen, the symptoms of cancer vary with the position of the tumour, as well as the size and stage of the tumour:

Tumor

Symptom

At right colon

Anaemia, abdominal mass, right sided abdominal pain, altered blood in stool or tarry stool

At left colon

Change in bowel habit, frequent bowel motions, decrease in caliber of stool, bowel obstruction

At rectum

Blood and mucus in stool, sense of incomplete emptying of motion

Spread to peritoneal cavity

Abdominal distension due to ascites

Spread to liver

Right upper abdominal pain, palpable abdominal mass

Diagnostic Investigations

After consultation and clinical examination, if the doctor suspects colorectal cancer, colonoscopy examination with biopsy should be performed. If the biopsy result confirmed the diagnosis of colorectal cancer, the patient should undergo further investigations to check if the tumour has spread to distant organs, these investigations include computed tomography scan (CT scan) or positron emission tomography scan (PET scan).

Staging of Disease
Endoscopic view of colon cancer
Colon Cancer – CT Scan image
Liver metastasis of colon cancer
– CT Scan image
Anatomy of colon and rectum

The most recognized and adopted classification system for colorectal cancer is the TNM staging. T represents the depth of invasion of the tumour, N represents the number of lymph nodes involved by the tumour and M represents the presence or absence of metastasis (distant spread):

T (Tumour): subdivided into four stages according to the depth of invasion to bowel wall.

  1. T1:invades submucosa
  2. T2:invades muscularis propria
  3. T3:invades subserosa
  4. T4:invades adjacent organs or penetrates visceral peritoneum

N (Node): represents the number of lymph nodes involvement, according to the guideline published by the American Society of Clinical Oncology (ASCO), at least 11 lymph nodes should be examined in order to have an accurate staging.

  1. N0:no involvement of lymph node
  2. N1:1-3 lymph nodes involved
  3. N2:4 or more lymph nodes involved

M (Metastasis): describes the presence of distant metastasis.

  1. M0:no metastasis
  2. M1:metastasis to distant organs, such as the liver, lungs, bone, peritoneal cavity and brain

The stage of the disease depends on the combination of T, N and M as below:

Stage of disease

TNM

I

T1N0M0 or T2N0M0

II

T3N0M0 or T4N0M0

III

Any T, N1 or N2 and M0

IV

Any T, any N, M1

For example, even the tumour invaded deeply, as T3 or T4, if there is no distant spread and no lymph node involvement, the patient belongs to stage I or II disease, surgery alone is curative, and chemotherapy is not necessary in most of the cases.
The stage of the disease governs the chance of relapse after treatment. The 5-year disease free rate for stage I, II and III diseases are 90%, 70% and 50% respectively. Statistics showed that chemotherapy given to stage III patients after surgery confers survival benefit.

Treatment

The only curative treatment for colon cancer is surgery, that is to remove the segment of colon containing the tumour, the vessels and lymphatic drainage of the territory. The resected tissue is then examined to look for any involvement of the lymph nodes. After treatment, the patient should regularly get clinical check up at a 3-month interval, including blood test and regular colonoscopy examination, to look for any possibility of relapse.