The colon and the rectum make up the ‘large bowel’ which is a 6 to 8 cm wide tube that leads to the anus. It takes mostly already digested food residue after it has passed through the small bowel, and extracts water form it. The rectum stores faeces before it can be emptied. The large bowel wall is made up largely glandular tissue, and it is from these cells that bowel cancer usually arises. The cancer usually develops though a stepwise process developing from normal tissue, into a polyp then on to cancer. The rate at which is occurs is variable.
Environmental factors and genetic factors have been found to cause colorectal cancer.
Familial Adenomatous polyposis is an inherited condition where multiple polyps develop in the colon during childhood. They usually cause symptoms by the age of 16 and if left untreated will develop into cancer in most cases across the next 20 years. The condition is caused by a mistake in a gene, called the ‘adenomatous polyposis coli gene’.
Hereditary nonpolyposis colorectal cancer, also called the ‘Lynch Syndrome’, is a genetic condition that causes colorectal cancer at a younger than normal age, and tends to affect the first half of the colon. Multiple polyps are not present. The condition is also associated with an increased risk of cancers of the ureter, pancreas, bile ducts, small bowel, stomach, ovary and womb.
Other risk factors
A diagnosis of Ulcerative Colitis:
Patients with Ulcerative Colitis have an increased risk of colon cancer, particularly if the whole colon is affected. If patients have ‘primary sclerosing cholangitis’ as well, the risk is increased further.
A Diagnosis of Insulin Dependent Diabetes:
It has been found that this diagnosis can multiply the risk of developing colon cancer by a factor of 1.3.
This increases the risk of cancer of the colon and rectum significantly if more than 3 or 4 units of alcohol are taken a day.
Being very overweight increases the risk of colorectal cancer by 50%.
Active smoking (as opposed to passive smoking) seems to increase the risk of rectal cancer.
Eating plenty of fruit and vegetables may be protective against colorectal cancer and red meat may increase the risk. However, there is some doubt as to whether this is really true. The role of fibre and folic acid as protective factors is also controversial although garlic and eating oily fish have been show to help.
Aspirin, Hormone Replacement Therapy, and Statins (used for lowering cholesterol) may reduce the risk of colorectal cancer.
Colorectal cancer is the third leading cause of death from cancer in both males and females in Western society at present comprising 11% of all cancers. There is a nearly identical incidence in males and females, but a slight relative higher frequency of rectal cancer in males (in Western society).
The cancers of the colon and rectum will be considered together as many aspects of their occurrence, histopathological origin and behaviour are identical, although important differences in therapy will be highlighted. Colorectal cancer has an annual incidence in Western society of 500 per million of the population and deaths due to this disease are second only to lung cancer in men and breast cancer in women. By contrast the disease is relatively rare in Africa. Colon cancer is now 2.4 times as common as rectal cancer a change from 30 years ago when rectal cancer was relatively more common.
Rectal cancer is defined as a cancer that arises below the peritoneal reflection or more simply more than 12-15 cm from the anus.
Symptoms & diagnosis: Colon and rectal cancer
The cancer can cause symptoms by either bleeding or causing disruption of the normal bowel function or by affecting organs it may have spread to.
- Abdominal Pain
- Blood from the back passage, often mixed in with the stools, but not always
- A loss of appetite
- Non deliberate weight loss
- A change in bowel habit
- A permanent feeling of having to empty the bowel (called tenesmus)
- Faecal incontinence
- Passing mucous from the bottom
- Anaemia (a low amount of red blood in the circulation)
A digital examination of the rectum is part of the routine examination of the rectum by every doctor and should be able to palpate the majority of rectal cancers.
A faecal occult blood test should alert the doctor to a bleeding lesion (not necessarily a tumour) in the bowel.
However, the most important test is the proctoscopy and colonoscopy where the doctor directly visualises the entire rectum and colon and is able to biopsy (take for analysis) any parts of the lining wall (the site of origin of all cancers) that look suspicious for cancer.
An indirect alternative to examine the large bowel is the barium enema where the colon is filled with radio-opaque barium solution such that a negative image is projected on x-ray film and any irregularities of the colonic wall are noted.
The biopsy for microscopic (histological) analysis is taken at the time of the colonoscopy and once the diagnosis is established, then a CT scan of the abdomen, pelvis and chest is performed to determine if the disease has spread.
Pre-operative staging will include the proctoscopy (the direct visualisation of the rectum through a telescopic apparatus) or colonoscopy (the same fibre optic telescopic system for the colon) with biopsy and then abdominal scanning, particularly looking for local spread outside the bowel and the liver, and the chest by chest x-ray.
Following operation, which, in this disease, may still go ahead even if there is early evidence of metastatic spread (to forestall bowel obstruction) the most important aspects for staging are given by the pathologist’s report. The pathologist (histologist) will comment on whether the tumour is confined to the inner bowel wall (stage A) or into the superficial bowel wall without reaching the outer coat (the serosa in the case of the colon) = stage B1, or whether there is full penetration through the bowel wall with local extension through into the surrounding tissues (stage B2). If the lymph nodes in the operative specimen are involved then the staging is C and if there is evidence of spread to other organs then the patient is referred to as having metastatic colorectal cancer.
These staging categories are important as they influence the treating doctors as to which patients are at higher risk of subsequent relapse and who should receive adjunctive post-operative therapy. The staging A-C being progressively less favourable with five year survivals of 80% for stage A, 60% for stage B and 30% for stage C; less than 5% of patients presenting with overt metastatic disease will be alive at five years.
Treatment & outcomes: Colon and rectal cancer
The treatment of colorectal cancer varies according to the stage of the disease and whether the aim of treatment is cure, or aimed at improving and to maintain the quality of life.
When the aim is cure
This is possible if the tumour has not spread to other organs and the patient is fit enough for treatment. If the tumour has spread to a small amount of the liver and nowhere else, cure may still be possible.
The main curative treatment is an operation, with other treatments given before and/or after the operation to improve the chances of cure.
For rectal cancer, the best operation is called a Total Mesorectal Excision, where the rectum is removed with a good safety margin around it, and is kept intact. If the tumour is very close to the anus, it is impossible to safely get below the cancer and leave enough uninvolved rectum to allow a ‘joining up’ operation to be performed. The lower rectum and anus are therefore removed the patient needs a permanent colostomy i.e. the bowel drains through a stoma that is brought out onto the anterior abdominal skin wall, emptying into a bag. The perineum – where the anus previously was – is sewn over. This operation is called an abdoperineal resection/excision (APR or APE).
In recent years, improved surgical technique has allowed surgeons to perform ‘joining up’ operations for lower rectal cancers. These are called anterior resections and the bowel above the cancer is sewn to the bowel below the resected cancer, so there is no need for a permanent colostomy.
The success of an operation for rectal cancer depends on the surgeon being able to remove the whole tumour with a safety margin around it. When the initial scans are done, it may be seen that this is not possible. When this is the case the tumour may be shrunk first by a course of radiotherapy and chemotherapy, given at the same time. This usually lasts 5 to 5 1/2 weeks and the chemotherapy is given continuously throughout this time. The operation can then be done, usually 6 to 12 weeks after the end of the chemo-radiotherapy. A temporary colostomy may be done before this to make the treatment easier to go through or if there are difficult symptoms that need dealing with quickly.
Sometimes, even if the tumour looks like it can be removed completely, a short course of radiotherapy, given daily for 5 days, is offered. The surgery is done the following week. This has been shown to reduce the risk of the disease returning in the same place.
For colon cancer, the operation depends on the site of the tumour but only certain operations are possible due to the blood supply to normal colon.
For cancers of the caecum and ascending colon a right hemicolectomy is performed. For those arising in the transverse colon a transverse colectomy is performed and a left hemicolectomy for those arising in the descending and sigmoid colon. In each case the bowel is joined up end-to-end such the patient comes out of the procedure with a normal functioning bowel. Sometimes if the patient has bowel obstruction due to the tumour, the surgeon may leave in a temporary colostomy above the operation site, until the bowel has settled.
After the operation, the resected tumour is analysed and the true stage is decided. If there are tumour cells in any of the lymph nodes or of the tumour extends into any nearby tissues, then a course of chemotherapy may reduce the chance of the disease returning. The choice of chemotherapy depends on the age and fitness of the patient. It will usually last for 6 months, given as a day case every 2 or 3 weeks.
There is no routine role for post-operative radiotherapy in the therapy of colon cancer cases.
In rectal cancer, the choice of whether to give chemotherapy after surgery is similar to that of colon cancer, but this is controversial. Radiotherapy may be given if the patient did not receive it preoperatively.
When the aim is to prolong and maximise the quality of life: Palliative treatment
If the tumour has spread to other organs then, generally, it is not possible to cure the disease. The choice of treatment approach in such cases is tailored to each patient individually; surgery, radiotherapy and chemotherapy may be useful, but the down sides and side effects must be considered with respect to the potential benefit.
Often chemotherapy is given, with the aim of shrinking and controlling the tumour. The choice of chemotherapy depends on whether and which treatment has been given before, and how long ago it was given. The side effects of chemotherapy drugs vary, and these may influence which is chosen.
Surgery may be used if the tumour is at risk of causing bowel obstruction, or a stent may be use to hold the bowel open to prevent or relieve obstruction.
Radiotherapy may be used to help shrink tumours that are causing symptoms, particularly in the rectum.
The outcome depends on the stage of the disease and the behaviour of the tumour. It is impossible to predict exactly what will happen to an individual patient and the figures are more often useful to help guide treatment to give the best chance of cure or improve quality of life. In general, the earlier the stage of the disease, the better the chances of cure. If the disease has spread, the disease cannot usually be cured.
Screening for colon and rectal cancer
Screening is recommended in those patients who have a positive family history of colorectal cancer (see the section on ‘Incidence’). Regular colonoscopies and rectal examinations should start in early adult or even late teenage life where there is a significant genetic risk.
The routine use of faecal occult blood screening (the examination of three stool specimens by a smear test that picks up traces of blood mixed in with the stool) for everyone between the ages of 60 an 69 is being rolled out in the UK (NHS Bowel Screening Programme) because it has been shown to reduce the risk of dying from bowel cancer by 16%.