Definition of Colorectal Cancer

Colorectal CancerMalignant growths in the colon, most commonly in the sigmoid colon and the rectum.

Colorectal cancer is the second-leading cause of death due to cancer in the United States.

However, colorectal cancer is also one of the most preventable and, with early detection, among the most treatable kinds of cancer.

More than 95 percent of primary colorectal cancer is adenocarcinoma, a form of cancer in which abnormal but otherwise benign growths (adenomas) become cancerous. Intestinal polyps are adenomas that develop in the colon, growing from the mucous membrane that lines the colon.

Intestinal polyps become more common with increasing age, and by age 50, about half of American adults are likely to have them.

Types of Polyps

There are two common types of colon polyps: adenomas, which are neoplastic (abnormal growths that have no useful function within the body) and have malignant potential, and hyperplastic, which are not neoplastic and have no malignant potential.

A polyp takes 5 to 10 years to grow from microscopic to detectable, and up to several decades to become cancerous, if that is its course. People who have no exceptional risk factors for colorectal cancer typically have a window of 5 to 10 years during which the polyp’s cell structure is transitional. Doctors consider such a polyp precancerous.

Though only a small percentage of intestinal polyps will become cancerous, there is no way to distinguish those that will from those that will remain benign. As a precaution doctors recommend removing all intestinal polyps, which eliminates any concerns about their potential malignancy.

Symptoms and Diagnostic Path

Early colorectal cancer has few, if any, symptoms, further emphasizing the importance of regular screening. When present, symptoms often indicate a cancer that is moderately to significantly advanced and include

  • Change in bowel habits or the nature of bowel movements
  • Unexplained nauseavomitingdiarrhea, or constipation
  • Rectal bleeding (may be patches of dark discoloration or bright bleeding)
  • Sensations of abdominal fullness or bloating
  • Tiredness and fatigue
  • Unintended weight loss
  • Abdominal distention and pain

The most effective way to detect and diagnose colorectal cancer is through regular screening procedures, which may include

  • Digital rectal examination (dre), in which the doctor inserts a gloved, lubricated finger into the rectum via the anus to feel for abnormalities
  • Fecal occult blood test (fobt), in which a laboratory tests a stool sample for microscopic blood (home-testing kits are also available)
  • Double-contrast barium enema, in which the radiologist instills barium into the lower colon via an enema, then takes X-rays as the barium fills the rectum and sigmoid colon
  • Sigmoidoscopy, in which the doctor inserts a lighted viewing tube (rigid or flexible) through the anus into the rectum and sigmoid colon, the two segments of the colon nearest the end of the intestinal tract and the sites where more than half of colorectal cancers originate
  • Colonoscopy, in which the doctor inserts a lighted, flexible viewing tube through the anus and into the entire colon (done under sedation)
  • Virtual colonoscopy (CT colonography)

Sigmoidoscopy (for the lower colon) and colonoscopy (for the full length of the colon) allow the gastroenterologist to detect and remove intestinal polyps and to biopsy suspicious growths. The gastroenterologist may use colonoscopy to explore suspicious findings from other screening procedures.

Further diagnostic procedures may include transrectal or abdominal ultrasound, computed tomography (ct) scan, and magnetic resonance imaging (mri).

Pathology examination of the suspect tissue confirms the diagnosis and establishes the extent of the cancer, a clinical classification process called staging of cancer. Staging identifies how far the cancer has spread, determines treatment recommendations and protocols, and establishes expectations about how the cancer will respond to treatment (prognosis).

The higher the stage number, the more advanced the cancer.

Basic Staging of Colorectal Cancer

Basic Staging of Colorectal Cancer
StageMeaningTreatment Protocol
stage 0cancer is in its earliest stages, completely confined to the polyp; also called carcinoma in situ or intramucosal carcinomasurgery to remove the cancerous polyp (polypectomy), typically via colonoscopy
stage 1cancer involves but remains confined to the inner layers of the intestinal mucosasurgery to remove the tumor and the involved segment of colon (local excision)
stage 2cancer extends beyond the wall of the colon but not into the lymph nodessurgery to remove the tumor and involved segment of colon; occasionally radiation therapy or chemotherapy
stage 3cancer extends beyond the wall of the colon and into nearby lymph nodessurgery to remove the tumor, the involved segment of colon, the surrounding tissue into which the cancer has spread, and the involved lymph nodes; radiation therapy or chemotherapy
stage 4cancer has spread to other organssurgery to remove tumors and involved tissues when possible; radiation therapy and/or chemotherapy
recurrenta return of the cancer to the colonsurgery to remove the tumor and involved segment of colon; radiation therapy and/or chemotherapy

Treatment Options and Outlook

Surgery is the first course of treatment for nearly all colorectal cancers. In cancers detected early, surgery often cures the cancer. Depending on the location and extent of the cancer, the surgeon can usually remove the cancerous tissue (called a bowel resection) and reconnect the healthy ends of the colon so the colon continues to function normally.

Sometimes the colon needs first to heal from the resection, in which case the surgeon performs a temporary colostomy that allows the colon to pass fecal matter through an opening created in the abdomen. When the colon heals, the surgeon reconnects the ends and closes the colostomy. Extensive cancer may make necessary a permanent colostomy.

The oncologist may recommend radiation therapy to shrink large tumors before surgery or to kill any cancerous cells remaining after surgery, primarily for cancer located in the rectum. Chemotherapy kills cancer cells that may have spread beyond the local tumor, and is the followup treatment of choice for cancers that involve lymph nodes.

Often the oncologist will recommend a combination of therapies. Oncologists also typically offer people who have stage 2 through stage 4 colorectal cancer the opportunity to participate in clinical research studies of new treatments. It is important to fully understand the benefits and risks of the investigational treatment.

Treatments for cancer offer varying benefits and risks

Cancer experts often recommend obtaining a second opinion evaluation from another physician specialist before making treatment decisions. Treatment is highly successful for colorectal cancers detected before they spread beyond the wall of the bowel. Stage 0 colorectal cancer is nearly always curable, and more than 90 percent of people diagnosed with stage 1 colorectal cancer are cancer-free five years after treatment.

The course of advanced and recurrent colorectal cancer is more challenging, and often results in moderate to significant lifestyle changes. Recovery from extensive surgery may take several months, and radiation therapy and chemotherapy typically cause numerous and varied side effects that often limit participation in regular activities.

Though the outlook for colorectal cancer continues to improve with early detection and new treatment technologies, it remains a serious health condition that requires appropriate and diligent attention. Cancer support groups provide excellent opportunities to share experiences and feelings in a protected setting.

Colorectal Cancer Screening Procedures

Colorectal Cancer Screening Procedures
ProcedureFrequencyBenefitsDrawbacks or Risks
digital rectal examination (dre)annually after age 45can detect growths and abnormalities in the rectumdoes not detect very small growths or growths beyond the rectum
further procedures required to investigate positive results
fecal occult blood test (fobt)annually after age 50detects microscopic blood in the stool, often while the growth causing the bleeding is still very small; sample collected at home; home-testing kits availablethe growth is large enough to cause bleeding by the time of detection
compliance is low
further procedures required to investigate positive results
sigmoidoscopyevery 5 years for those with average risk; every 3 years for those with increased riskprovides direct examination of the walls of the rectum and sigmoid colon; doctor can remove or biopsy detected polyps or tumorsdoes not visualize full length of the colon
unpleasant preparation
some discomfort during the procedure
minimal risk of infection, bleeding, or perforation
further procedures required to investigate positive results
double-contrast barium enemaevery 10 years for those with average risk; every 5 years for those with increased riskprovides clear representation of the full colondoes not detect very small polyps or tumors
less effective in detecting polyps or tumors in the rectum than in the colon
unpleasant preparation
some discomfort during the procedure
further procedures required to investigate positive results
colonoscopyevery 10 years for those with average risk; every 5 years for those with increased riskallows direct examination of the full colon; doctor can remove or biopsy detected polyps or tumorsunpleasant preparation
some discomfort during the procedure
requires general sedation

Risk Factors and Preventive Measures

The most significant risk factor for colorectal cancer, as for many kinds of cancer, is age.

Doctors diagnose more than 90 percent of colorectal cancer in people who are age 50 and older.

Health and medical factors that present increased risk include

Lifestyle factors that appear to increase the risk for colorectal cancer include a diet high in saturated fats (animal-based fats) and low in fruits and vegetables, lack of daily physical exercise, and smoking.

Regular screening is the most effective preventive measure for colorectal cancer.

Cancer experts recommend colonoscopy as the first line of screening for colorectal cancer in most people starting at age 50, though earlier in people with family members who have had colorectal cancer at an earlier age, every 10 years for people with average risk and every 5 years for people with additional risk factors. Research suggests such screening could eliminate 80 to 90 percent of colorectal cancer.

Though conclusive evidence of dietary correlations to risk for intestinal polyps and colorectal cancer remains elusive, cancer experts encourage a diet high in natural fiber (especially fresh fruits and vegetables) and low in saturated fat. Other lifestyle recommendations include daily physical exercise, smoking cessation, and weight management.


Colorectal Cancer – Definition, Staging, Symptoms and Treatment
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