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Colorectal Cancer

(Colon Cancer; Rectal Cancer)


Anthony Villano

, MD, Fox Chase Cancer Center

Reviewed/Revised Oct 2023
Topic Resources

Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal involvement. Behavioral measures and possibly low-dose aspirin may decrease risk.

Colorectal cancer is the 4th most commonly diagnosed cancer in the United States. Incidence rises sharply around age 40 to 50. In 2023, an estimated 106,970 new cases of colon cancer and 46,050 new cases of rectal cancer will be diagnosed (1 General references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more General references ). The number of colorectal cancer deaths has steadily decreased in the last several decades and is believed to be the result of improved screening and diagnosis at earlier stages of disease.

Overall, more than half of the cases occur in the rectum and sigmoid, and 95% are adenocarcinomas. Colorectal cancer is slightly more common among men than women. Synchronous cancers (more than one) occur in about 5% of patients (2 General references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more General references ).

General references

Etiology of Colorectal Cancer

Colorectal cancer (CRC) most often occurs as transformation within adenomatous polyps Polyps of the Colon and Rectum An intestinal polyp is any mass of tissue that arises from the bowel wall and protrudes into the lumen. Most are asymptomatic except for minor bleeding, which is usually occult. The main concern... read more Polyps of the Colon and Rectum . About 80% of cases are sporadic, and 20% have an inheritable component. Many genetic syndromes predispose to CRC:

Patients in populations with a high incidence of CRC eat low-fiber diets that are high in animal protein, fat, and refined carbohydrates. Carcinogens may be ingested in the diet but are more likely produced by bacterial action on dietary substances or biliary or intestinal secretions. The exact mechanism is unknown.

CRC spreads by direct extension through the bowel wall, hematogenous metastasis, regional lymph node metastasis, and perineural spread.

Symptoms and Signs of Colorectal Cancer

Colorectal adenocarcinomas grow slowly, and a long interval elapses before they are large enough to cause symptoms. Symptoms depend on lesion location, type, extent, and complications.

The right colon has a large caliber and a thin wall and its contents are liquid; thus, obstruction is a late event. Bleeding is usually occult. Fatigue and weakness caused by severe anemia Evaluation of Anemia Anemia is a decrease in the number of red blood cells (RBCs) as measured by the red cell count, the hematocrit, or the red cell hemoglobin content. In men, anemia is defined as any of the following... read more Evaluation of Anemia may be the only complaints, and tumors are often asymptomatic and are detected only when colonoscopy or cross-sectional imaging is done for another reason. Tumors sometimes grow large enough to be palpable through the abdominal wall before other symptoms appear.

The left colon has a smaller lumen, the feces are semisolid, and cancer tends to cause obstruction earlier than in the right colon. Partial obstruction with colicky abdominal pain or complete obstruction may be the initial manifestation. The stool may be streaked or mixed with blood. Some patients present with symptoms of perforation, usually walled off (focal pain and tenderness), or rarely with diffuse peritonitis.

Diagnosis of Colorectal Cancer

  • Colonoscopic biopsy

  • CT to evaluate extent of tumor growth and spread

  • Genetic testing

Patients who have symptoms that suggest colon cancer or who have a positive screening test Colorectal Cancer Screening For average-risk patients, screening for colorectal cancer (CRC) should begin at age 45 years and continue until age 75 years. For adults aged 76 to 85, the decision whether to screen for CRC... read more need a diagnostic test to confirm whether they do or do not have cancer. Current guidelines recommend screening for all people, regardless of risk factors.

Patients with positive fecal occult blood tests or positive fecal DNA tests require colonoscopy, as do those with lesions seen during sigmoidoscopy or an imaging study. All lesions should be completely removed for histologic examination. If a lesion is sessile or not removable at colonoscopy, surgical excision should be strongly considered to rule out an occult cancer.

Barium enema x-ray Barium enema X-ray and other imaging contrast studies visualize the entire gastrointestinal tract from pharynx to rectum and are most useful for detecting mass lesions and structural abnormalities (eg, tumors... read more Barium enema , particularly a double-contrast study, can detect many lesions but is somewhat less accurate than colonoscopy and is not currently acceptable as follow-up to a positive fecal occult blood test or positive DNA test.

Once cancer is diagnosed, patients should undergo complete imaging staging with CT of the chest, abdomen, and pelvis and routine laboratory tests to seek metastatic disease and anemia and to evaluate overall condition.

Elevated serum carcinoembryonic antigen (CEA) levels are present in 70% of patients with CRC. CEA level is routinely obtained as part of the initial evaluation for CRC, but this test is neither sensitive nor specific and therefore is not recommended for screening purposes. However, if the CEA level is high preoperatively and low after removal of a colon tumor, monitoring the level may help detect recurrence earlier.

Colon cancers that were removed during surgery are now routinely tested for the gene mutations that cause Lynch syndrome Lynch Syndrome Lynch syndrome is an autosomal dominant disorder responsible for 2 to 3% of cases of colorectal cancer ( 1). Symptoms, initial diagnosis, and treatment are similar to other forms of colorectal... read more . People with relatives who developed colon, ovarian, or endometrial cancer at a young age or who have multiple relatives with those cancers should be tested for Lynch syndrome. Patients with confirmed Lynch syndrome or with a family history concerning for Lynch syndrome are referred for genetic counseling.

Treatment of Colorectal Cancer

  • Surgical resection, sometimes combined with chemotherapy, radiation, or both


Surgical resection is the mainstay for curative-intent treatment of CRC. Resection consists of removal of the anatomic segment of the large intestine harboring the tumor along with its regional lymphatic drainage. In general, a wide, 5-cm margin is planned, but a negative margin of any distance is acceptable. Resection is typically followed by reconnection of the bowel segments to restore enteral continuity (anastomosis).

For rectal cancer, sphincter-sparing surgical resection (low anterior resection) can be done in patients with low tumors near, but not involving, the anal sphincter complex without significant risk of local recurrence or decreased long-term survival. Sphincter-sparing procedures necessitate a low anastomosis, which often is followed by functional issues postoperatively (eg, fecal leakage, incontinence). If there is local recurrence or poorly tolerated bowel function after a sphincter-sparing procedure, an abdominoperineal resection (APR) with permanent colostomy is usually recommended (1 Treatment references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more Treatment references ).

  • Number of metastatic lesions in the liver

  • Amount of liver parenchyma involved with metastatic disease

  • Resectability of the involved segments of the liver

  • Synchronous vs metachronous presentation

  • Tumor biology (presence of KRAS, NRAS, or BRAF mutations)

Patients with liver metastases should be evaluated for treatment options by a multidisciplinary team that includes medical oncologists, radiation oncologists, interventional radiologists, and hepatobiliary surgeons. A multidisciplinary team is critical to the treatment decision-making process.

Adjuvant therapy

In colon cancer, postoperative chemotherapy is indicated for patients with stage III disease (lymph node-positive) or patients with high-risk stage II disease (lymph node-negative but high-risk features seen on pathology such as lymphovascular invasion) (see table ).

In general, patients who are stage T3 or T4 or who are suspected of having nodal disease will receive both chemotherapy and chemoradiation in conjunction with surgical resection.


After curative surgical resection of colorectal cancer, surveillance colonoscopy should be done 1 year after surgery or after the clearing preoperative colonoscopy (5 Treatment references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more Treatment references ). A second surveillance colonoscopy should be done 3 years after the 1-year surveillance colonoscopy if no polyps or tumors are found. Thereafter, surveillance colonoscopy should be done every 5 years. If the preoperative colonoscopy was incomplete because of an obstructing cancer, a completion colonoscopy should be done 3 to 6 months after surgery to detect any synchronous cancers and to detect and resect any precancerous polyps (5 Treatment references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more Treatment references ).

Additional screening for recurrence should include history, physical examination, and serum carcinoembryonic antigen levels every 3 months for 3 years and then every 6 months for 2 years.

Imaging studies (CT or MRI) are done every 6 to 12 months for 5 years.


When curative surgery is not possible or the patient is an unacceptable surgical risk, limited palliative surgery (eg, to relieve obstruction or resect a perforated area) may be indicated; median survival is 7 months. Some obstructing tumors can be debulked by electrocoagulation or held open by stents. Chemotherapy may shrink tumors and prolong life for several months.

Chemotherapy drugs, used singly or in combinations, include capecitabine (a 5-fluorouracil precursor), irinotecan, and oxaliplatin. Monoclonal antibodies such as bevacizumab, cetuximab, and panitumumab are also used selectively with some effectiveness. No regimen is clearly more effective for prolonging life in patients with metastatic CRC, although some regimens delay disease progression. Chemotherapy for advanced colon cancer should be managed by an experienced medical oncologist who has access to investigational medications or clinical trials.

When metastases are confined to the liver but cannot be surgically resected, hepatic artery infusion with floxuridine or radioactive microspheres, given either intermittently in a radiology department or given continuously via an implantable subcutaneous pump or an external pump worn on the belt, may offer more benefit than systemic chemotherapy; however, these therapies are of uncertain benefit, and clinical trials are underway to understand their relative benefits and harms. Stereotactic radiation therapy or thermal ablation using radiofrequency or microwave treatments also can be considered for palliation.

Treatment references

  • 1. Bujko K, Rutkowski A, Chang GJ, et al: Is the 1-cm rule of distal bowel resection margin in rectal cancer based on clinical evidence? A systematic review. Ann Surg Oncol 19(3):801–808, 2012. doi: 10.1245/s10434-011-2035-2

  • 2. Garcia-Aguilar J, Patil S, Gollub MJ, et al: Organ preservation in patients with rectal adenocarcinoma treated with total neoadjuvant therapy. J Clin Oncol 40(23):2546–2556, 2022. doi: 10.1200/JCO.22.00032

  • 3. Bahadoer RR, Dijkstra EA, van Etten B, et al: Short-course radiotherapy followed by chemotherapy before total mesorectal excision (TME) versus preoperative chemoradiotherapy, TME, and optional adjuvant chemotherapy in locally advanced rectal cancer (RAPIDO): A randomised, open-label, phase 3 trial. Lancet Oncol 22(1):29–42, 2021. doi: 10.1016/S1470-2045(20)30555-6. Clarification and additional information. Lancet Oncol 22(2):e42, 2021.

  • 4. Conroy T, Bosset JF, Etienne PL, et al: Neoadjuvant chemotherapy with FOLFIRINOX and preoperative chemoradiotherapy for patients with locally advanced rectal cancer (UNICANCER-PRODIGE 23): A multicentre, randomised, open-label, phase 3 trial. Lancet Oncol 22(5):702–715, 2021. doi: 10.1016/S1470-2045(21)00079-6

  • 5. Kahi CJ, Boland R, Dominitz JA, et al: Colonoscopy surveillance after colorectal cancer resection: Recommendations of the US multi-society task force on colorectal cancer. Gastroenterology 150:758–768, 2016. doi: 10.1053/j.gastro.2016.01.001

Prognosis for Colorectal Cancer

Prognosis depends greatly on stage (see table ).

The 5-year survival rate for cancer limited to the mucosa approaches 90%; with extension through the bowel wall, 70 to 80%; with positive lymph nodes, 30 to 50%; and with metastatic disease, < 20%.


Staging Colorectal Cancer*


Tumor (Maximum Penetration)

Regional Lymph Node Metastasis

Distant Metastasis






T1 or T2








Any T




Any T

Any N


* TNM classification:

  • Tis = carcinoma in situ; T1 = submucosa; T2 = muscularis propria; T3 = penetrates all layers (for rectal cancer, includes perirectal tissue); T4 = adjacent organs or peritoneum.

  • N0 = none; N1 = 1–3 regional nodes or any number of tumor deposits without nodal involvement; N2 = 4 regional nodes.

  • M0 = none; M1 = present.

Prevention of Colorectal Cancer

  • Modification of environmental factors

  • Sometimes low-dose aspirin

  • Physical inactivity

  • Obesity

  • Tobacco exposure

  • Excess ingestion of red and processed meat

  • Low-fiber diet

  • Excess alcohol consumption

The USPSTF also recommends the use of low-dose aspirin as primary prevention of cardiovascular disease and CRC in adults who have an average risk of CRC and who meet all of the following (2 Prevention references Colorectal cancer is extremely common. Symptoms include blood in the stool and change in bowel habits. Diagnosis is by colonoscopy. Treatment is surgical resection and chemotherapy for nodal... read more Prevention references ):

  • Age 50 to 59 years

  • ≥ 10% risk of 10-year atherosclerotic cardiovascular disease (see calculator )

  • No increased risk of bleeding

  • Life expectancy ≥ 10 years

  • Willingness to take low-dose aspirin daily for ≥ 10 years

Whether to use low-dose aspirin for adults meeting the same criteria except for an age 60 to 69 should be decided by shared decision-making.

Prevention references

  • 1. Martínez ME: Primary prevention of colorectal cancer: Lifestyle, nutrition, exercise. Recent Results Cancer Res 166:177-211, 2005. doi: 10.1007/3-540-26980-0_13

  • 2. Bibbins-Domingo K; U.S. Preventive Services Task Force: Aspirin Use for the Primary Prevention of Cardiovascular Disease and Colorectal Cancer: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med 164(12):836-845, 2016. doi: 10.7326/M16-0577

Key Points

  • Colorectal cancer is one of the most common cancers in western countries, typically arising within an adenomatous polyp.

  • Right-sided lesions usually manifest with bleeding and anemia; left-sided lesions usually manifest with obstructive symptoms (eg, colicky abdominal pain).

  • Routine screening should begin at age 45 for patients with average risk; typical methods involve colonoscopy or annual fecal occult blood testing and/or flexible sigmoidoscopy.

  • Serum carcinoembryonic antigen (CEA) levels are often elevated but are not specific enough to be used for screening; however, after treatment, monitoring CEA levels may help detect recurrence.

  • Treatment is with surgical resection, sometimes combined with chemotherapy and/or radiation; outcome varies widely depending on the stage of the disease.

  • Behavioral measures (eg, physical activity, dietary changes, avoiding tobacco or excess alcohol) and sometimes low-dose aspirin may decrease risk.

Drugs Mentioned In This Article

Drug Name Select Trade
Adrucil, Carac, Efudex, Fluoroplex, Tolak
Alymsys, Avastin, MVASI, Zirabev
Anacin Adult Low Strength, Aspergum, Aspir-Low, Aspirtab , Aspir-Trin , Bayer Advanced Aspirin, Bayer Aspirin, Bayer Aspirin Extra Strength, Bayer Aspirin Plus, Bayer Aspirin Regimen, Bayer Children's Aspirin, Bayer Extra Strength, Bayer Extra Strength Plus, Bayer Genuine Aspirin, Bayer Low Dose Aspirin Regimen, Bayer Womens Aspirin , BeneHealth Aspirin, Bufferin, Bufferin Extra Strength, Bufferin Low Dose, DURLAZA, Easprin , Ecotrin, Ecotrin Low Strength, Genacote, Halfprin, MiniPrin, St. Joseph Adult Low Strength, St. Joseph Aspirin, VAZALORE, Zero Order Release Aspirin, ZORprin
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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