Colorectal (bowel) cancer is the growth of rapidly dividing abnormal cells in the colon or rectum. It is the second most commonly occurring internal cancer in Australia with about 17 000 new cases arising every year. It is slightly more common in males.
The exact cause of colorectal cancer is not known. It occurs through a combination of genetic changes (some inherited and some acquired). Most cancers arise from colonic polyps (a benign growth) and it takes multiple genetic changes for cancer to arise. The time it takes for this process can be 5 – 10 years thus making screening for polyps and removing them a very worthwhile endeavour.
Risk factors for the development of colorectal cancer include:
Colorectal cancer can remain without symptoms for a prolonged period of time. Symptoms that develop include rectal bleeding (usually mixed with stool), a change in bowel habits (increased constipation or diarrhoea), bowel obstruction or symptoms of anaemia (increased fatigue, lethargy).
This is usually made at colonoscopy where the cancer can be visualised and biopsied. Further tests including a CT scan of the abdomen and chest will be used to see if the cancer had spread outside the bowel to other organs (most commonly liver and lungs). An MRI pelvis is used to locally stage a rectal cancer.
Colorectal cancer starts in the mucosa (lining) of the bowel. The cancer spreads through the muscle of the bowel wall, to the lymph nodes adjacent to the bowel and then eventually to other organs. There are 4 stages:
The primary treatment of colorectal cancers is surgery. In most cases, the aim of treatment is cure although this is dependent on the stage. All cancer cases are discussed at a multidisciplinary meeting with specialist opinions given by surgeons, medical oncologists, radiation oncologists, radiologists, pathologist as well as allied health professionals.
Surgery involves the removal of the cancer along with a portion of normal bowel on either side. Along with the bowel, the draining lymph nodes (glands) are also removed and tested for cancer. The ends of the bowel can be re-joined in most instances forming an anastomosis.
These ‘keyhole’ techniques can be used in the majority of colorectal cancer cases. They have the advantages of less post operative discomfort, shorter hospital stay, minimal incisions and earlier return to normal activities and work. The cancer outcomes between open and laparoscopic surgery are equivalent.
A stoma is where the bowel is brought out through the abdominal wall into a bag. A permanent stoma is nowadays quite uncommon with improved surgical techniques. It is needed for extremely low rectal cancers that are close to the anal sphincters. A temporary stoma is used for mid and lower rectal cancers (to protect the anastomosis) and can usually be reversed after a few months.
Chemotherapy is used in colon cancer after surgery in stage 3 cancers (occasionally in stage 2) to try and minimise the risk of recurrence.
Radiation (and chemotherapy) is used pre-operatively in mid and low rectal cancers that are at high risk of local recurrence
Five year survival in Australia is nearing 70% for all stages. Prognosis is stage dependent and early stages have the highest cure rates.
Follow-up is done for five years. A typical follow-up regime is: