Colorectal cancer

Synonyms	Colon cancer, rectal cancer, bowel cancer
Pronounce	N/A
Field	Gastroenterology General surgery Oncology
Symptoms	Blood in stool
Complications
Onset
Duration
Types	N/A
Causes	Lifestyle factors and genetic disorders
Risks	Diet obesity smoking lack of physical activity alcohol and cancer
Diagnosis	Tissue biopsy during a sigmoidoscopy or colonoscopy
Differential diagnosis
Prevention	Screening from age of 45 to 75
Treatment	Surgery radiation therapy chemotherapy targeted therapy
Medication
Prognosis	Five-year survival rate 65% (US)
Frequency	9.4 million (2015)
Deaths	551,000 (2018)

Colon and rectum cancers world map-Deaths per million persons-WHO2012

Colon cancer with extensive metastases to the liver

A diagram of a local resection of early stage colon cancer

A diagram of local surgery for rectal cancer

Margins of a colonic resection.

Longitudinally opened freshly resected colon segment showing a cancer and four polyps

Micrograph of colorectal adenocarcinoma, showing "dirty necrosis".

Relative incidence of various histopathological types of colorectal cancer

Colorectal cancer (CRC), also known as colon cancer or rectal cancer, is a type of cancer that affects the colon or rectum, which are parts of the digestive system. It is one of the most common cancers globally and a leading cause of cancer-related deaths.

Epidemiology

Colorectal cancer is the third most commonly diagnosed cancer worldwide and the second leading cause of cancer mortality. Its incidence is higher in developed countries, particularly in North America, Europe, and Australia. Men are slightly more likely than women to develop the disease, and risk increases with age, typically after the age of 50.

Risk Factors

Several factors can increase the risk of developing colorectal cancer, including:

Lifestyle Factors:

• Diet high in red or processed meats
• Low fiber intake
• Obesity
• Physical inactivity
• Alcohol consumption and smoking

Medical and Genetic Factors:

• Personal history of inflammatory bowel disease (IBD) such as Crohn's disease or ulcerative colitis
• Family history of colorectal cancer
• Genetic conditions like Lynch syndrome or familial adenomatous polyposis (FAP)

Environmental Factors:

• Exposure to certain carcinogens
• Geographic variations in incidence linked to diet and healthcare access

Pathophysiology

Colorectal cancer typically begins as a benign growth called a polyp on the inner lining of the colon or rectum. Over time, some polyps may develop into cancer. The most common types of polyps associated with colorectal cancer are:

• Adenomatous polyps (adenomas): These can become cancerous.
• Hyperplastic polyps and inflammatory polyps: These are generally non-cancerous but may increase risk in specific scenarios.

The progression from normal tissue to adenoma and then to carcinoma is often driven by genetic mutations in key tumor suppressor genes and oncogenes.

Signs and Symptoms

Symptoms of colorectal cancer may vary depending on the tumor's location and size. Common symptoms include:

• Changes in bowel habits, such as diarrhea or constipation
• Presence of blood in stool or rectal bleeding
• Abdominal pain or cramping
• Unintended weight loss
• Fatigue and weakness due to anemia (often from chronic bleeding)

Diagnosis

The diagnosis of colorectal cancer involves a combination of clinical evaluation, imaging studies, and laboratory tests. Common diagnostic methods include:

Screening Tests:

• Colonoscopy: Gold standard for detecting and removing polyps.
• Fecal immunochemical test (FIT): A non-invasive stool test.
• CT colonography: A less invasive imaging technique.

Imaging Studies:

• CT scan or MRI to determine the extent of the disease.
• PET scan to detect metastases.

Biopsy:

• Tissue samples are taken during colonoscopy for histopathology.

Staging

Colorectal cancer is staged using the TNM staging system, which evaluates:

• T (Tumor): Size and invasion of the primary tumor.
• N (Nodes): Spread to nearby lymph nodes.
• M (Metastasis): Spread to distant organs like the liver or lungs.

Stages range from I (localized) to IV (advanced with metastases).

Treatment

Treatment depends on the stage of the cancer and may involve a combination of the following:

Surgery:

• Colectomy or proctectomy to remove the affected portion of the colon or rectum.

Laparoscopic surgery or robotic-assisted surgery for minimally invasive approaches.

Chemotherapy:

• Drugs like 5-fluorouracil and oxaliplatin are used to destroy cancer cells, often in advanced stages.

Radiation Therapy:

• Often used for rectal cancer to shrink tumors before surgery or to treat residual cancer.

Targeted Therapy:

• Drugs like bevacizumab (anti-VEGF) or cetuximab (anti-EGFR) may be used in metastatic disease.

Immunotherapy:

• Checkpoint inhibitors like nivolumab and pembrolizumab for certain genetic subtypes.

Prevention

Preventive strategies include:

Lifestyle Changes:

• Consuming a diet rich in fiber, fruits, and vegetables.
• Regular physical activity.
• Avoiding smoking and excessive alcohol consumption.

Screening:

• Regular colonoscopy screening starting at age 45 for average-risk individuals.
• Earlier and more frequent screening for high-risk individuals.

Medications:

• In certain cases, aspirin or other NSAIDs may reduce the risk of colorectal cancer.

Prognosis

The prognosis for colorectal cancer depends on the stage at diagnosis:

• Early-stage cancers (Stage I or II) have a 5-year survival rate of over 90%.
• Advanced cancers with distant metastases (Stage IV) have a lower survival rate, typically around 14%.

Research and Advances

Recent advances in colorectal cancer research include:

• Development of new biomarkers for early detection.
• Personalized medicine approaches using genomic profiling.
• Enhanced surgical techniques, such as robotic surgery.
• Ongoing trials for novel immunotherapies.

See Also

• Gastrointestinal cancer
• Polyps
• Digestive system diseases

References

For more detailed information, visit:

• American Cancer Society guidelines on colorectal cancer.

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