Bowel Cancer: Cancer of the Colon and Rectum

Bowel cancer arises within the colon or rectum and often develops from a precancerous polyp over several years. It may be found after symptoms or through FIT based screening before symptoms appear. Diagnosis, stage and tumour biology determine whether treatment aims for cure or long term disease control.

What bowel cancer is Bowel cancer is cancer arising within the large bowel. The large bowel includes the colon and rectum. Cancer in these locations is also called colorectal cancer. Most colorectal cancers are adenocarcinomas. They begin in gland forming cells lining the bowel. Cancer can grow through the bowel wall, enter lymphatic or blood vessels and spread elsewhere. Cancer of the anus and cancer of the small bowel are different diseases with separate pathways. The colon and rectum have different roles The colon absorbs water and moves bowel contents towards the rectum. The right colon includes the caecum and ascending colon. The transverse colon crosses the upper abdomen. The left colon includes the descending and sigmoid colon. The rectum stores stool before it leaves through the anus. Tumour location affects symptoms, imaging, surgery and the role of radiotherapy. Most cancers develop over time Many colorectal cancers develop through the adenoma carcinoma sequence. An adenoma is a type of polyp formed by abnormal glandular cells within the bowel lining. Some adenomas gradually accumulate genetic and cellular changes. A minority eventually become invasive cancer. This progression usually takes years, which creates an opportunity to find and remove precancerous polyps. Not every adenoma becomes cancer, and not every bowel cancer follows this pathway. Other pathways to bowel cancer Some colorectal cancers arise through a serrated pathway involving particular serrated polyps. Others develop in the setting of inherited syndromes or longstanding inflammatory bowel disease. A cancer can occasionally appear without a previously recognised polyp. The adenoma carcinoma sequence is therefore a durable main model, not a universal rule. What a bowel polyp is A polyp is a growth projecting from the inner bowel lining. Most polyps are benign and never cause symptoms. Adenomatous and some serrated polyps have greater potential to become cancer over time. Colonoscopy can remove many polyps before cancer develops. The polyp's size, number and microscopic features guide whether future surveillance is needed. Risk increases with age Bowel cancer risk rises with age, although younger adults can also develop the disease. A health problems in the family can increase risk, especially when relatives were diagnosed young or several relatives are affected. Longstanding ulcerative colitis or Crohn's colitis increases risk because persistent inflammation can alter bowel cells. Smoking, alcohol, obesity, physical inactivity and diets high in processed meat can contribute to risk. Risk factors change probability. They do not diagnose cancer or explain every individual case. Inherited predisposition Lynch syndrome is the most common inherited cause of colorectal cancer. It results from a harmful inherited change affecting DNA mismatch repair. Familial adenomatous polyposis causes numerous adenomas and a very high untreated cancer risk. Most people with bowel cancer do not have one of these high risk inherited syndromes. Age at diagnosis, tumour testing and health problems in the family guide referral to genomic services. Early disease may cause no symptoms Small cancers and advanced polyps can develop without noticeable symptoms. Some are found through the NHS Bowel Cancer Screening Programme. Others are discovered incidentally during imaging, colonoscopy or surgery performed for another reason. Screening detected disease still requires colonoscopy, biopsy and staging before treatment is planned. Rectal bleeding Blood may appear bright red, dark red or mixed through the stool. Rectal bleeding commonly results from haemorrhoids, fissures, diverticular disease or inflammation. Visible blood does not reveal where bleeding started or whether cancer is present. Persistent or unexplained bleeding requires assessment, particularly when combined with bowel change, pain, weight loss or anaemia. Black tar like stool may indicate bleeding higher in the digestive tract and needs urgent assessment. A change in bowel habit Bowel cancer can alter how often someone passes stool and its usual consistency. Possible changes include persistent looser stool, constipation, alternating patterns or needing to go more often. Rectal disease can create urgency or a feeling that the bowel has not emptied fully. Infection, medicines, diet, irritable bowel syndrome and inflammatory bowel disease are much more common causes. A persistent unexplained change should be assessed rather than diagnosed from stool appearance alone. Abdominal pain and bloating A tumour can cause discomfort by narrowing the bowel, stretching tissues or affecting nearby structures. Pain may be vague, cramping or colicky. Bloating and abdominal swelling can occur when bowel contents and gas do not pass normally. Most abdominal pain and bloating are not caused by cancer. Severe pain with vomiting, swelling or inability to pass stool or wind may indicate obstruction. Unexplained weight loss and appetite change Bowel cancer can cause reduced appetite and unintentional weight loss. Weight loss may result from inflammation, reduced intake, obstruction or advanced disease. These symptoms are non specific and occur in many physical and mental health conditions. Persistent weight loss requires assessment, especially when combined with bleeding, bowel change or abdominal pain. Iron deficiency anaemia A bowel tumour can bleed slowly without producing visible blood. Repeated small losses may deplete iron and cause iron deficiency anaemia. Symptoms include fatigue, breathlessness, palpitations, headaches and pale skin. Anaemia may be the only recognised presentation of bowel cancer. Menstrual bleeding, diet, upper gastrointestinal bleeding and other conditions remain important alternative causes. An abdominal or rectal mass A clinician may feel an abdominal mass during examination. A digital rectal examination can sometimes identify a low rectal tumour. A palpable mass has several possible causes, including stool, enlarged organs and benign bowel disease. An unexplained rectal mass can justify direct suspected cancer referral without waiting for FIT. Right sided colon cancer Right sided cancers arise in the caecum, ascending colon or nearby transverse colon. The right colon has a wider lumen, and its contents remain relatively liquid. A tumour can therefore bleed slowly and grow substantially before causing complete obstruction. Iron deficiency anaemia, fatigue, vague right sided discomfort, weight loss or an abdominal mass may be prominent. Visible rectal bleeding and obstruction can still occur. Left sided colon cancer Left sided cancers arise in the descending or sigmoid colon. The bowel lumen is narrower and stool is more solid in this region. These cancers may cause a persistent bowel habit change, colicky pain, visible blood or progressive narrowing. Large bowel obstruction is particularly associated with left sided tumours, although obstruction can occur elsewhere. Location based patterns are tendencies and cannot identify the tumour site reliably at home. Rectal cancer symptoms Rectal cancer often causes bleeding, urgency and a repeated feeling of incomplete emptying. Some people pass mucus or notice narrower stool, but stool shape is not a reliable diagnostic sign. Low rectal tumours may be felt during rectal examination. Pelvic pain, urinary symptoms or altered sexual function can occur with locally advanced disease. Haemorrhoids can coexist with cancer, so an apparent benign cause does not always end assessment. Symptoms can overlap Right sided, left sided and rectal cancers do not follow fixed symptom rules. A right sided cancer can cause visible bleeding or obstruction. A left sided cancer can present mainly through anaemia. The purpose of these patterns is to explain variation, not to locate cancer from symptoms. Screening and symptomatic pathways are different Screening looks for hidden blood in people who do not have concerning bowel symptoms. The symptomatic pathway investigates a specific clinical concern such as bleeding, bowel change, anaemia or weight loss. Both pathways use a test called FIT, but their thresholds, context and next steps are not identical. A negative screening result does not replace assessment of new symptoms. NHS bowel cancer screening in England The NHS Bowel Cancer Screening Programme in England invites people aged 50 to 74 every two years. Eligible people registered with a GP receive a home FIT kit by post. People aged 75 or over can request a kit every two years but are not automatically invited. Screening arrangements differ across the UK nations, so local programme information should be checked. What screening FIT measures The faecal immunochemical test is usually shortened to FIT. It measures human haemoglobin in a small stool sample. Polyps and bowel cancers can release tiny amounts of blood that are not visible. A result above the programme threshold leads to further assessment, usually discussion about colonoscopy. FIT does not identify the source of blood and does not diagnose cancer. Benefits and limitations of screening Screening can find cancer before symptoms develop, when treatment may be more effective. It can also find polyps that can be removed before they become cancer. Most people with a positive FIT do not have bowel cancer. FIT can miss cancers that are not bleeding when the sample is collected. Colonoscopy can also miss an abnormality, particularly when bowel preparation or visualisation is incomplete. Screening detected bowel cancer Screening detected cancers are found after a positive programme FIT in someone without concerning symptoms. They are often diagnosed at an earlier stage, although screening does not guarantee early disease. The person is offered colonoscopy or an alternative investigation when colonoscopy is unsuitable. Biopsy and staging follow the same cancer principles used after a symptomatic presentation. How a cancer was detected does not determine its exact biology or individual prognosis. Symptomatic bowel cancer Symptomatic cancer is found after a person or clinician notices a concerning change. Symptoms do not automatically mean that disease is advanced. Some early cancers bleed, while some advanced cancers cause few bowel symptoms. People should not wait for their next screening kit when symptoms are present. Primary care assessment A clinician asks about bleeding, bowel pattern, pain, weight, appetite and duration of symptoms. They review medicines, previous bowel disease, screening results and health problems in the family. Examination may include the abdomen and a digital rectal examination. A full blood count and iron studies can identify anaemia. FIT is now central to deciding referral for many symptomatic adults. Symptomatic FIT NICE recommends quantitative FIT for several bowel cancer presentations in primary care. These include change in bowel habit, iron deficiency anaemia, an abdominal mass and several age related symptom combinations. FIT should still be offered when a previous NHS screening FIT was negative. A symptomatic FIT result must be interpreted with the examination, blood results and persistence of symptoms. The suspected cancer referral pathway The suspected cancer pathway is commonly called the two week wait pathway. NICE recommends referral when symptomatic FIT is at least 10 micrograms of haemoglobin per gram of faeces. A rectal mass can justify referral without waiting for FIT. Referral should not be delayed when strong clinical concern remains despite a lower FIT or an unreturned sample. This threshold guides clinicians and must not be used as a home self triage score. Safety netting after a lower FIT A FIT below the referral threshold makes colorectal cancer less likely but does not make it impossible. Bleeding can be intermittent, and some cancers release little detectable blood. Persistent, worsening or unexplained symptoms require review. The clinician may repeat assessment, arrange another investigation or refer despite the result. People must know when and how to seek further help. Urgent referral is not a diagnosis Most people referred through a suspected cancer pathway do not receive a cancer diagnosis. The pathway exists because timely investigation matters when risk is raised. Current NHS standards also aim to confirm or exclude cancer promptly after urgent referral. The referral should be explained without either false reassurance or unnecessary alarm. Colonoscopy Colonoscopy is the main test for examining the whole colon and rectum. A flexible camera passes through the anus while the person is usually awake with pain relief or sedation options. The bowel must be emptied using laxative preparation beforehand. The clinician can inspect the lining, remove many polyps and take biopsies. Colonoscopy can be uncomfortable and has small risks of bleeding and perforation. Biopsy and pathology A biopsy removes a small tissue sample from a suspicious area. A pathologist determines whether it contains cancer and identifies the histological type. Most colorectal cancers are adenocarcinomas. The report can describe grade and other features that help estimate behaviour. Imaging alone cannot provide the same microscopic information. CT colonography CT colonography uses CT images to examine the inside contour of the large bowel. It may be used when colonoscopy is incomplete, unsuitable or declined. Bowel preparation and inflation of the colon are still usually required. CT colonography cannot remove a polyp or take a biopsy. A suspicious finding generally leads to colonoscopy or surgery for tissue diagnosis. Staging scans After cancer is confirmed, CT of the chest, abdomen and pelvis assesses local and distant spread. Rectal cancer usually requires pelvic MRI for detailed local staging. MRI shows the tumour's relationship to the rectal wall, mesorectal fascia and nearby structures. Selected liver findings may need liver MRI, and PET CT is reserved for particular questions. Not every person needs every available scan. Carcinoembryonic antigen Carcinoembryonic antigen is usually shortened to CEA. A blood level may be measured around diagnosis to provide a baseline. CEA can help follow some people after potentially curative treatment. A normal CEA does not exclude bowel cancer. A raised result is not specific and can occur with smoking, inflammation and other cancers. Mismatch repair and microsatellite instability Colorectal cancers are tested for mismatch repair deficiency or high microsatellite instability. These features can suggest possible Lynch syndrome and guide further testing. They also provide prognostic information and can predict benefit from immunotherapy in advanced disease. A tumour abnormality does not automatically mean that the person inherited a gene change. Genetic assessment separates acquired tumour changes from inherited risk. Other molecular biomarkers Metastatic colorectal cancer is tested for treatment relevant changes such as RAS and BRAF V600E. These results help decide whether selected targeted medicines are likely to work. Cancer location and HER2 or NTRK findings may influence options in selected situations. Molecular treatment choices are made by specialist teams and change as evidence develops. What staging means Staging describes how far cancer has grown and spread. Clinical stage uses examination, imaging and biopsy information before definitive treatment. Pathological stage uses the bowel and lymph nodes removed during surgery. Stage influences prognosis, treatment sequence and whether the main intention is cure or disease control. It does not predict one person's outcome with certainty. TNM staging The TNM system is the modern standard for colorectal cancer staging. T describes how deeply the primary tumour has grown through the bowel wall or nearby structures. N describes whether regional lymph nodes contain cancer. M describes distant metastases. The TNM components combine into overall stages from I to IV. The older Dukes system The Dukes system is an older colorectal staging method that may still appear in records or discussions. Dukes A describes disease limited to the bowel wall, while Dukes B extends through it without involved nodes. Dukes C includes regional lymph node involvement. Dukes D describes distant spread. TNM provides more detail, and the systems do not map perfectly in every case. Stage I and II disease Stage I cancer has grown into the bowel wall but has not reached regional nodes or distant organs. Stage II cancer extends further through the wall or into nearby tissue without confirmed nodal spread. Surgery is the main curative treatment for most resectable stage I and II cancers. Selected higher risk stage II cancers may be offered chemotherapy after surgery. The decision uses pathology, mismatch repair status, fitness and personal preferences. Stage III disease Stage III cancer has reached regional lymph nodes but has no confirmed distant metastases. Treatment commonly includes curative surgery and postoperative chemotherapy. Rectal cancer may receive radiotherapy or chemoradiotherapy before surgery. Node positive disease is serious, but many people receive treatment with curative intent. Stage IV disease Stage IV cancer has spread to a distant site such as the liver, lungs or peritoneum. Treatment is often non curative and focuses on disease control, symptoms and survival. However, selected people with limited liver or lung metastases can receive surgery, ablation or stereotactic radiotherapy with curative intent. Stage IV therefore does not automatically mean that every treatment is palliative. Treatment intent Curative intent treatment aims to remove or eradicate all known cancer and microscopic disease. Palliative or non curative treatment aims to control cancer, relieve symptoms and prolong life when cure is not achievable. Palliative care can also support people receiving curative treatment. Treatment intent can change when new operative or staging information becomes available. The team should explain the aim clearly before treatment begins. Multidisciplinary planning Treatment is planned by a colorectal multidisciplinary team. This includes surgeons, radiologists, pathologists, oncologists and specialist nurses. Gastroenterologists, stoma clinicians, geneticists, liver surgeons and palliative care teams contribute when needed. The team combines tumour site, stage, pathology, molecular results, fitness and personal priorities. Surgery is the main curative treatment Surgery is the primary curative treatment for most localised colon and rectal cancers. The operation removes the tumour, a margin of bowel and its draining lymph nodes. The remaining bowel may be joined together in an anastomosis. Keyhole, robotic or open surgery may be used according to anatomy, expertise and clinical need. The final pathology determines the definitive stage and need for additional treatment. Colon cancer surgery Colon surgery usually removes the bowel segment containing the cancer and its blood supply. A right hemicolectomy removes the right colon, while a left or sigmoid colectomy treats left sided disease. The operation name reflects anatomy rather than cancer severity. Emergency surgery may be necessary for obstruction, perforation or uncontrolled bleeding. Some emergencies can be managed initially with a stent or temporary stoma. Rectal cancer surgery Rectal surgery must remove the cancer while protecting nearby pelvic structures where possible. Total mesorectal excision removes the rectum with its surrounding lymphatic tissue for many tumours. Very early selected cancers may be removed through the anus using local excision techniques. Low tumours sometimes require removal of the anus and a permanent colostomy. Other tumours can be removed while preserving the anal sphincter. A stoma A stoma brings bowel through an opening in the abdominal wall so waste enters a bag. A colostomy uses colon, while an ileostomy uses small bowel. A stoma may protect a new join while it heals, bypass an obstruction or become permanent after particular operations. Not everyone having bowel cancer surgery needs a stoma. A specialist stoma clinician provides marking, education and ongoing support. Radiotherapy and rectal cancer Radiotherapy has a particular role in rectal cancer because the rectum lies relatively fixed within the pelvis. Preoperative short course radiotherapy or chemoradiotherapy can reduce local recurrence risk and help control locally advanced disease. NICE recommends preoperative radiotherapy or chemoradiotherapy for node positive or more locally advanced rectal cancer. Early cT1 to cT2 node negative rectal cancer does not routinely receive preoperative radiotherapy. Treatment selection depends on MRI staging and multidisciplinary review. Why radiotherapy is less common in colon cancer The colon moves within the abdomen and lies near radiosensitive small bowel. Surgery and systemic treatment therefore provide the main curative approach for colon cancer. Radiotherapy is not routinely used around an ordinary resectable colon tumour. It can still treat selected metastases, recurrences or symptoms. Colon and rectal cancer should not be assumed to have identical radiotherapy pathways. Chemotherapy after surgery Adjuvant chemotherapy treats possible microscopic cancer remaining after apparently complete surgery. It is routinely offered to many people with stage III colon cancer. It is considered for selected higher risk stage II cancers. Regimens commonly use a fluoropyrimidine with or without oxaliplatin. Expected benefit is balanced against neuropathy, infection risk, organ function and individual fitness. Treatment before surgery Neoadjuvant treatment is given before an operation. Rectal cancer often receives radiotherapy, chemoradiotherapy or a sequence including systemic chemotherapy before surgery. Selected cT4 colon cancers may receive preoperative systemic anticancer treatment. The aims include shrinking disease, improving resectability and treating microscopic spread early. Treatment before surgery does not automatically mean that cancer is incurable. Systemic treatment for advanced disease Chemotherapy circulates through the body and can control cancer at several sites. Common combinations use fluoropyrimidines with oxaliplatin or irinotecan. Targeted medicines may block EGFR or blood vessel growth pathways in selected tumours. Immunotherapy can be highly effective for some mismatch repair deficient or MSI high cancers. The choice depends on biomarkers, previous treatment, tumour location, fitness and goals. Local treatment of metastases Some liver or lung metastases can be removed surgically. Ablation destroys selected lesions using heat, cold or another local technique. Stereotactic radiotherapy can treat suitable lung or other metastases. These options require specialist multidisciplinary review. Local treatment may aim for cure in selected people or control a troublesome site. Bowel obstruction A tumour can narrow the bowel until stool and gas cannot pass. Symptoms include colicky pain, increasing swelling, vomiting and inability to pass stool or wind. Complete obstruction is an emergency. Left sided obstruction may be treated with emergency surgery or a colonic stent. A stent can bridge to planned surgery or relieve obstruction during palliative care. Perforation and peritonitis Cancer can rarely create a hole in the bowel or cause the bowel to rupture above an obstruction. Bowel contents then leak into the abdomen and can cause peritonitis and sepsis. Possible features include sudden severe pain, a rigid abdomen, fever, collapse or confusion. Perforation requires emergency hospital treatment and usually surgery. Severe bleeding Most bowel cancer bleeding is slow or intermittent. Heavy bleeding can occasionally cause dizziness, fainting, breathlessness or shock. Continuous bleeding, large clots or toilet water turning red requires emergency assessment. Black or dark red stool and bloody diarrhoea require urgent clinical advice. Neutropenic sepsis Chemotherapy can reduce neutrophils, which normally help control bacterial infection. An infection can then become life threatening rapidly. People receiving systemic anticancer treatment receive an emergency contact number and temperature instructions. Fever, shaking chills, confusion or sudden severe illness requires immediate oncology assessment. A normal temperature does not always exclude neutropenic sepsis. Treatment side effects Surgery can cause pain, infection, anastomotic leakage, hernia and altered bowel function. Rectal surgery can affect urinary and sexual function because pelvic nerves lie nearby. Oxaliplatin can cause tingling, numbness and cold sensitivity. Radiotherapy can affect bowel frequency, urgency, skin and pelvic organs. Targeted therapy and immunotherapy have treatment specific toxicities requiring prompt reporting. Low anterior resection syndrome Sphincter preserving rectal surgery can alter bowel storage and control. Possible symptoms include frequent small stools, urgency, leakage and incomplete emptying. This pattern is called low anterior resection syndrome. Dietetic advice, medicines, pelvic floor support and specialist bowel management programmes can help. Preserving the anus does not always preserve the previous bowel pattern. Follow up after curative treatment Follow up looks for recurrence and supports recovery after treatment. NICE recommends CEA and CT surveillance during the first three years after potentially curative surgery. Colonoscopy checks for new polyps, another cancer and the remaining bowel. Schedules are individualised according to treatment and findings. New symptoms should be reported between planned appointments. Living with and after a stoma A stoma can alter body image, clothing, travel and intimate relationships. Modern appliances are designed to be secure and discreet. A temporary stoma may be reversed when healing and health allow. Some people experience skin irritation, blockage, high output or a parastomal hernia. Stoma support should be practical, respectful and available before and after surgery. Nutrition and recovery Bowel cancer and treatment can affect appetite, weight and nutrient intake. There is no single diet that treats bowel cancer. Dietary advice depends on obstruction risk, surgery, stoma output and treatment effects. A dietitian can help with weight loss, diarrhoea, constipation or food restriction. Unproven restrictive diets can worsen malnutrition and should not replace treatment. Emotional and practical effects Bowel cancer can affect continence, sexuality, employment and confidence outside the home. Fear of bleeding, urgency or stoma leakage can cause social isolation. Specialist nurses, psychological support and welfare advice can help. People should receive information in a form they can understand and use. There is no single correct emotional response to a cancer diagnosis. What this lesson should not be used for This lesson cannot diagnose bowel cancer from bleeding, anaemia, stool shape or a FIT result alone. It cannot determine tumour side, stage or treatment intent without endoscopy, pathology and imaging. Do not wait for screening when symptoms are present. Do not assume that a negative FIT or recent colonoscopy makes persistent symptoms unimportant. Seek medical assessment for unexplained bowel changes and emergency help for obstruction, perforation or heavy bleeding.

Most bowel cancers are adenocarcinomas arising in the colon or rectum, often after gradual change within an adenomatous polyp. Screening and symptomatic FIT serve different pathways. Colonoscopy and biopsy establish the diagnosis, while TNM stage and tumour biology guide surgery, chemotherapy, rectal radiotherapy and treatment intent.