Introduction
Background
Almost all colon cancers are primary adenocarcinomas, which are the third most common cancer in both men and women in North America and Western Europe.
Cecal carcinoma. A large polypoid cecal mass involves the ileocecal valve and causes small bowel obstruction.
Colon cancers are the most common gastrointestinal (GI) carcinomas and have the best prognosis. The 5-year survival rates of approximately 50% may be improved by screening and removal of adenomatous polyps.1
Pathophysiology
Tumors of the colon arise as intramucosal epithelial lesions, usually in adenomatous polyps or glands. As cancers grow, they invade the muscularis mucosa and lymphatic and vascular structures to involve regional lymph nodes, adjacent structures, and distant sites, especially the liver.2
Frequency
United States
Colorectal cancer is the third most common cancer diagnosis and the third leading cause of death from cancer. It is the most common GI cancer. The American Cancer Society has estimated that in 2008, over 148,000 people will be diagnosed with colorectal cancer and about 50,000 will die of colorectal cancer; 72% will occur in the colon and 28% in the rectum. About 96% colorectal cancers are adenocarcinomas.3
The highest rates of the disease are found in the northeastern and north central states, and the lowest rates are in the southern and western states (except the San Francisco Bay area and Hawaii).
The incidence of colon cancer has risen since 1950, while the incidence of rectal cancer has remained stable. The increased incidence of colon cancer is believed to be a result of an increased intake of fat and beef and a decreased intake of fiber.
International
The incidence of colon cancer is highest in the westernized countries of North America, Northern Europe, Australia, and New Zealand. Intermediate rates are found in Southern Europe, and low rates are found in Africa, Asia, and South America. A 60-fold difference exists between those areas with the highest incidence of colon cancer and those areas with the lowest incidence. More than 940,000 new cases of colorectal cancer and nearly 500,000 deaths associated with colorectal cancer are reported worldwide each year (World Health Organization, 2003).
Mortality/Morbidity
The prognosis of patients with colon cancer relates to the stage of the disease at the time of diagnosis and to initial treatment. Although a tumor, node, metastasis(TNM)–based international classification and a computed tomography (CT) staging system have been developed recently, the Dukes classification (or one of its modifications) is widely used (Table 1, below). Prognosis is also affected by the histologic grade of the tumor.
The complications of colon cancer include obstruction (common), perforation (uncommon), intussusception and ischemic colitis proximal to an obstructing tumor (rare), and fistula formation in the small bowel, bladder, or vagina (rare).
Table 1. Dukes Classification and 5-Year Survival* 4Open table in new window
Table
| Stage | Description | 5-Year Survival |
| A | Limited to the bowel wall | 83% |
| B | Extension to pericolic fat; no nodes | 70% |
| C | Regional lymph node metastases | 30% |
| D | Distant metastases (liver, lung, bone) | 10% |
| Stage | Description | 5-Year Survival |
| A | Limited to the bowel wall | 83% |
| B | Extension to pericolic fat; no nodes | 70% |
| C | Regional lymph node metastases | 30% |
| D | Distant metastases (liver, lung, bone) | 10% |
*Modified from Zinkin.4
Several factors increase the risk for colonic cancer.
- High-fat, low-fiber diet
- Patient age greater than 50 years
- Personal history of colorectal adenoma or carcinoma (3-fold risk)
- First-degree relative with colorectal cancer (3-fold risk)
- Familial polyposis coli, Gardner syndrome, and Turcot syndrome (all patients develop colorectal carcinoma unless they undergo a colectomy)
- Juvenile polyposis syndrome, Peutz-Jeghers syndrome, and Muir-Torre syndrome (risk increased slightly)
- Hereditary nonpolyposis colorectal cancer (as many as 50% of patients are affected)
- Inflammatory bowel disease
- Ulcerative colitis (risk is 30% after 25 years)
- Crohn disease (4- to 10-fold risk)
Race
International incidences reflect dietary differences in fat and fiber intake rather than racial differences. When a developing country adopts a Western diet, colon cancer rates rise. Similarly, immigrants from a low-incidence country soon experience the approximate incidence rate of their adopted country.
Sex
Males and females are equally affected.
Age
Of patients with colon cancer, 90% are older than 50 years. The highest incidence rates are in individuals aged 70-85 years. Only 10% of patients are younger than 50 years.
Anatomy
The colon is 150 cm long and is subdivided into the cecum and the ascending, transverse, descending, and sigmoid colons. The ileocecal valve forms the junction between the small and large bowel and demarcates the cecum from the ascending colon. The transverse and sigmoid colons have a mesentery and are entirely intraperitoneal. The ascending and descending colons are partially extraperitoneal.
The superior mesenteric artery supplies the colon between the ileocecal valve and the splenic flexure. The inferior mesenteric artery supplies the colon distal to the splenic flexure. The colon wall comprises 4 layers, including the mucosa, submucosa, muscularis propria (inner circular layer and outer longitudinal layer, comprising 3 narrow bands), and serosa.
Presentation
Colon cancers progress slowly and may be asymptomatic for as many as 5 years; however, patients usually have occult blood loss from their tumors.
Symptoms depend on the location of the primary tumor. Cancers of the cecum and ascending colon usually grow larger than left-sided tumors before symptoms occur. Fatigue, shortness of breath, and angina resulting from microcytic hypochromic anemia are common presenting features. Vague abdominal discomfort or a palpable mass may occur later, but obstruction is uncommon (unless the ileocecal junction is involved) because of the larger diameters of the cecum and ascending colon.
Cancers of the descending and sigmoid colons may present with large bowel obstruction. Perforation is rare but may occur as a result of distention proximal to the tumor (usually in the cecum) or locally (at the site of the tumor). The primary tumor may be palpable in the abdomen. Overt rectal bleeding is more common in tumors of the sigmoid colon, whereas occult bleeding is typical with proximal tumors. A change in bowel habits may be the only presenting feature. Weight loss, jaundice, and ascites are associated with advanced metastatic disease.5
Signs and Symptoms:
- May be asymptomatic
- Microcytic hypochromic anemia (fatigue, shortness of breath, angina)
- Vague abdominal discomfort
- Change in bowel habit
- Palpable mass
- Rectal bleeding (overt or occult)
- Large bowel obstruction
- Perforation (rare)
- Jaundice
- Ascites
Preferred Examination
- Begin the evaluation with a history and physical examination, including a digital rectal examination.
- Inspect the stool, and test for occult blood.
- Perform blood tests, including a full blood count, liver function tests, and carcinoembryonic antigen (CEA) level.
- Perform either a sigmoidoscopy (rigid or flexible), along with a double-contrast barium enema study, or a colonoscopy.
- CT scan colonography or virtual colonoscopy, to evaluate the entire colon, is described in CT scan section of this article.
Limitations of Techniques
Sigmoidoscopy
The 60-cm flexible sigmoidoscope has greater range than the rigid sigmoidoscope, which, at best, only reaches the distal sigmoid (20 cm).
Double-contrast barium enema
A double-contrast barium enema study detects most colon tumors (80-95%); however, flexible sigmoidoscopy should precede the barium enema as it is more accurate in detecting small rectal lesions. The double contrast barium enema has a low perforation rate (1 in 25,000).
Colonoscopy
Colonoscopy detects more adenomatous polyps than a barium enema, and polyps can be excised during the procedure. Colonoscopy is approximately 3 times more expensive, has a much higher perforation rate (1 in 1700) than barium enema, and fails to reach the cecum in 5-30% of patients.
Differential Diagnoses
Colitis, Ischemic
Colon, Diverticulitis
Colon, Polyps
Crohn Disease
Tuberculosis, Gastrointestinal
Ulcerative Colitis
Other Problems to Be Considered
Colon lymphoma
Metastases to the colon
More on Colon, Adenocarcinoma |
 Overview: Colon, Adenocarcinoma |
| Imaging: Colon, Adenocarcinoma |
| Follow-up: Colon, Adenocarcinoma |
| Multimedia: Colon, Adenocarcinoma |
| References |
| Further Reading |
| Next Page » |
References
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Further Reading
Related eMedicine topics
Colon Cancer, Adenocarcinoma
Colorectal Tumors
Colonoscopy
Gastrointestinal Bleeding, Lower
Gastrointestinal Stromal Tumors - Leiomyoma/Leiomyosarcoma
Guidelines
Colorectal Cancer Screening and Surveillance: Clinical Guidelines and Rationale—Update Based on New Evidence
Management of Colorectal Cancer: A National Clinical Guideline
Clinical studies
Combination Chemotherapy in Treating Patients with Advanced Colorectal Cancer
Combination Chemotherapy in Treating Patients with Liver Metastases from Colorectal Cancer
Keywords
colon adenocarcinoma, adenocarcinoma of colon, carcinoma of the colon, colon cancer, colorectal cancer
