Colon cancer is extremely common with around 30,000 cases per year diagnosed in the UK alone.This makes it one of the top three most common cancers for men and women. It is more common in the elderly (over 70) but occasionally it can occur in very young people. It is also a little more common in men than women.
Genetic Colon Cancer
Around 5% colon cancers may have an inherited or genetic component, and you may be aware of this if colon cancer runs in your family. There are two conditions – Familial Adenomatous Polyposis (FAP) and Hereditary Non-Polyposis Colon Cancer (HNPCC) which can run in families. Your oncologist will be aware of these and arrange further tests if necessary. This is important as your family will need careful screening if you do have one of these conditions. The vast majority of colon cancers (95%) occur spontaneously and there is little we can do to stop it at the moment.
Certain medical conditions can also increase the risk of colon cancer. Inflammatory bowel disease (ulcerative colitis or Crohns disease) can be one, but these patients are normally under close surveillance by their doctors. Smoking has only a weak link with colon cancer.
There is some evidence that eating more fresh fruit and vegetables (5 a day) can reduce the risk of contracting colon cancer. The link is probably very weak but we all like to encourage healthy eating to reduce the risk of other conditions like diabetes and heart disease. There is also mounting evidence that taking a small dose of aspirin every day may help prevent colon cancer. It has no effect however once the cancer has developed.
Colorectal cancer can take many years to develop and early detection greatly improves the chance of a cure. Therefore, screening for the disease is recommended in individuals who are at increased risk. There are several different tests available for this purpose. There is now a national screening programme for bowel cancer being rolled out across the country. This is for the over 60’s. The programme involves a test on a sample of your faeces to check for microscopic amounts of blood (called a faecal occult blood test). If positive it is normally recommended that you have a colonoscopy (telescope examination of the bowel). Ask your GP for further details.
The first symptoms of colon cancer are usually vague, like bleeding, weight loss, and fatigue (tiredness). Local (bowel) symptoms are rare until the tumour has grown to a large size. Generally, the nearer the tumour is to the anus, the more bowel symptoms there will be such as pain and a dragging sensation or a feeling of incomplete emptying after you have been to the toilet.
Symptoms and signs are divided into local, constitutional and metastatic.
- Change in bowel habit
- Change in frequency (constipation or diarrhoea),
- Feeling of incomplete emptying after defecation (tenesmus) and reduction in diameter of motion, both characteristic of rectal cancer,
- Change in the appearance of stools:
- Bloody stools or rectal bleeding
- Stools with mucous
- Black, tar-like stool (melaena), more likely related to upper gastrointestinal eg stomach disease
- Bowel obstruction causing bowel pain, bloating and vomiting of stool-like material. This is usually an emergency situation requiring admission through A&E and an immediate operation to relieve the obstruction.
- A mass in the abdomen, felt by patients or their doctors.
Constitutional (systemic) symptoms
- Unexplained weight loss, probably the most common symptom, caused by lack of appetite.
- Anaemia, causing dizziness, fatigue, shortness of breath on exertion, and palpitations. There will be paleness and blood tests will confirm the low hemoglobin level.
Diagnosis, and monitoring
If your doctor suspects a colon cancer you will undergo several tests.
- digital rectal examination (doctor examines lower bowel with a gloved finger)
- colonoscopy – telescope examination of the whole large bowel. Requires laxative preparation and often done under sedation. Biopsies can be taken to confirm the diagnosis.
- Endoanal ultrasound – Sometimes done for rectal or anal cancers to provide information on the depth of invasion of tumour into the muscles, and information on whether lymph nodes are involved.
- blood tests – to look for anaemia, liver function, kidney function, and tumour marker blood tests (CEA, Ca19.9)
- CT Scan – Chest, abdomen, pelvis. This is to confirm the location of the primary tumour and to look for evidence of spread to other organs or lymph nodes. This is an x-ray scan which gives high resolution cross sectional images through the body. Often you have to drink sime special fluid before the scan, and an injection of contrast is given, to show up the bowel and blood vessels more clearly. If you are allergic to x-ray contrast media or iodine please let your doctor know.
- MRI Scan – This is a magnetic scan which gives very clear images. It is done for tumours low down in the bowel (rectum, anus) to deliver information on how easily the tumour can be removed surgically. It is also used to assess the effects of radiotherapy to the pelvis for anal and rectal cancers. Sometimes it can be used to image the liver if the CT scan has picked up something suspicious but it is unclear.
- PET scan. This is a highly specialised scan which is only done on some patients. An injection of radioactive sugar is given. Cancer cells are more active as they are dividing rapidly and so preferentially take up the radioactive sugar. A special camera (called a gamma camera) can pick up the emissions from the radioactive sugar within cancer cells and a picture of the cancer distribution within the body is produced. This test is usually only performed if there is uncertainty from other tests whether cancer has spread, or to confirm the cancer has not spread if major surgery (e.g. to the liver or lungs) is being considered.
The pathology of the tumour is usually reported from the analysis of tissue taken from a biopsy or surgery which is analysed under the microscope. A pathology report will usually contain a description of cell type and grade. The most common colon cancer cell type is adenocarcinoma which accounts for 95% of cases. Other, rarer types include lymphoma, squamous cell carcinoma, carcinoid, melanoma, and small cell carcinoma
Cancers on the right side (ascending colon and caecum) tend to be exophytic, that is, the tumour grows outwards from one location in the bowel wall. This very rarely causes obstruction, and presents with symptoms such as anaemia. Left-sided tumours tend to be circumferential, and can obstruct the bowel much like a napkin ring.
Colon cancer staging is an estimate of how advanced any particular cancer is. It is performed for diagnostic purposes, and to determine the best method of treatment. The systems for staging colorectal cancers largely depend on the extent of local invasion, the degree of lymph node involvement and whether there is distant spread.
Definitive staging can only be done after surgery has been performed and pathology reports reviewed. Preoperative staging of rectal cancers may be done with MRI and endoanal ultrasound.
Dukes classification, first proposed by Dr Cuthbert Dukes in 1932, identifies the stages as:
- A – Tumour confined to the intestinal wall lining
- B – Tumour invading through the intestinal wall lining into muscle
- C – With lymph node(s) involvement
- D – With distant metastasis
The most common current staging system is the TNM (tumours/nodes/metastases) system, though many doctors still use the older Dukes system. The TNM system assigns a number:
T – The degree of invasion of the intestinal wall
- T0 – no evidence of tumour
- T1 – invasion through submucosa
- T2 – invasion into the muscle layer
- T3 – invasion through the muscle into surrounding fatty tissue
- T4 – invasion of surrounding structures (e.g. bladder) or with tumour cells on the free external surface of the bowel
N – the degree of lymph node involvement
- N0 – no nodes involved
- N1 – one to three nodes involved
- N2 – four or more nodes involved
M – Metastases (distant spread)
- M0 – no metastasis
- M1 – metastasis present
The treatment depends on the staging of the cancer. When colorectal cancer is caught at early stages (with little spread) it can be curable. However when it is detected at later stages (when distant metastases are present) it is less likely to be curable.
Surgery remains the primary treatment while chemotherapy and/or radiotherapy may be recommended depending on the individual patient’s staging and other medical factors.
Surgeries can be categorised into curative, palliative, bypass, faecal diversion, or open-and-close.
Curative surgical treatment can be offered if the tumour is localized.
Very early cancer that develops within a polyp can often be cured by removing the polyp (i.e., polypectomy) at the time of colonoscopy. In colon cancer, a more advanced tumour typically requires surgical removal of the section of colon containing the tumour with sufficient margins, and resection of mesentery (fatty lining of bowel containing lymph nodes) to reduce local recurrence (i.e., colectomy).
If possible, the remaining parts of colon are joined together to create a functioning colon. In cases when anastomosis is not possible, a stoma (artificial orifice) is created. Usually these stomas are temporary to allow the bowel to heal up properly before the ends are joined back together. Tumours lower down in the bowel (rectum) have a poorer blood supply and take longer to heal, so a temporary stoma is often needed for these. If the tumour is very low down and the whole anal canal needs to be removed then a permanent stoma is necessary.
Curative surgery on rectal cancer includes total mesorectal excision (low anterior resection) or abdominoperineal resection.
In case of multiple metastases, palliative (non curative) resection of the primary tumour is still offered in order to reduce further symptoms caused by tumour bleeding and invading. Surgical removal of isolated liver metastases is, however, common and may be curative in selected patients; improved chemotherapy has increased the number of patients who are offered surgical removal of isolated liver metastases. Removal of lung metastases is also now possible.
If the tumour invaded into adjacent vital structures (T4) which makes excision technically difficult, the surgeons may prefer to bypass the tumour (ileotransverse bypass) or to do a proximal faecal diversion through a stoma.
The worst case would be an open-and-close surgery, when surgeons find the tumour unresectable and the small bowel involved; any more procedures would do more harm than good to the patient. This is uncommon with the advent of laparoscopy and better radiological imaging. Most of these cases formerly subjected to “open and close” procedures are now diagnosed in advance and surgery avoided.
Laparoscopic (keyhole) surgery is a minimally invasive technique that can reduce the size of the incision and may reduce post-operative pain. It is increasingly used for bowel resections.
As with any surgical procedure, colorectal surgery may result in complications including
- wound infection, Dehiscence (bursting open of wound) or hernia
- anastomosis breakdown, leading to abscess or fistula formation, and/or peritonitis
- Adhesions resulting in bowel obstruction
- Adjacent organ injury; most commonly to the small intestine, ureters, spleen, or bladder
- Cardiorespiratory complications such as heart attack (rare), pneumonia, blood clots.
Treatment of liver metastases
Around 25% of patients present with metastatic (stage IV) colorectal cancer at the time of diagnosis, and up to 25% of this group will have isolated liver metastasis that is potentially resectable. Lesions which undergo curative resection have demonstrated 5-year survival outcomes now exceeding 50%
Resectability of a liver metastasis is determined using preoperative imaging studies (CT or MRI), intraoperative ultrasound, and by direct palpation and visualization during resection. Lesions confined to the right lobe are amenable to en bloc removal with a right hepatectomy (liver resection) surgery. Smaller lesions of the central or left liver lobe may sometimes be resected in anatomic “segments”, while large lesions of left hepatic lobe are resected by a procedure called hepatic trisegmentectomy. Treatment of lesions by smaller, non-anatomic “wedge” resections is associated with higher recurrence rates. Some lesions which are not initially amenable to surgical resection may become candidates if they have significant responses to preoperative chemotherapy regimens. Lesions which are not amenable to surgical resection for cure can be treated with modalities including radio-frequency ablation (RFA), cryoablation, and chemoembolization.
More recently CyberKnife radiosurgery has been developed as a minimally invasive way of destroying liver metastases whilst avoiding major surgery, and can also be used to treat ‘surgically inoperable’ metastases close to major blood vessels etc.
Patients with colon cancer and metastatic disease to the liver may be treated in either a single surgery or in staged surgeries (with the colon tumour traditionally removed first) depending upon the fitness of the patient for prolonged surgery, the difficulty expected with the procedure with either the colon or liver resection, and the comfort of the surgery performing potentially complex hepatic surgery.
The aims of follow-up are to diagnose in the earliest possible stage any recurrence or metastasis or tumours that develop later but did not originate from the original cancer (metachronous lesions).
A medical symptom history and physical examination are recommended every 3 to 6 months for 2 years, then every 6 months for 5 years. CEA tumour marker blood level measurements follow the same timing, but are only advised for patients with T2 or greater lesions. A CT scan of the chest, abdomen and pelvis is considered annually for the first 2 – 3 years. A colonoscopy can be done after 5 years.
Routine PET scan or ultrasound, are not recommended.
Aspirin should not be taken routinely to prevent colorectal cancer, even in people with a family history of the disease, because the risk of bleeding and kidney failure from high dose aspirin (300mg or more) outweigh the possible benefits. Consult your GP for advice.