Colon cancer: what it is, main causes and how to identify symptoms

Colon cancer, also known as colorectal cancer, is a type of cancer that begins in the large intestine (colon), which is the final part of the digestive tract. Colon cancer typically affects older adults, though it can occur at any age. It usually begins as small, benign (noncancerous) clumps of cells called polyps that form on the inside of the colon. Over time, some of these polyps can become colon cancers.

Polyps may be small and produce few, if any, symptoms. For this reason, doctors recommend regular screening tests to help prevent colon cancer by identifying and removing polyps before they turn into cancer.

How Colon Cancer Develops

Colon cancer, or colorectal cancer, develops in a multi-step process that typically starts with the formation of polyps in the lining of the colon or rectum. Not all polyps become cancerous, but certain types, particularly adenomatous polyps (adenomas), have a higher risk of transforming into cancer over time. Understanding how colon cancer develops is crucial for prevention and early detection strategies. Here’s an overview of the process:

1. Initiation of Polyps: The process begins with the growth of polyps in the colon's lining. Polyps are benign growths that can arise due to genetic mutations in the cells of the colon lining. These mutations cause cells to divide uncontrollably, leading to the formation of polyps. There are several types of polyps, but adenomas are the most common type related to colon cancer.

2. Genetic Mutations: As these adenomatous polyps grow, further genetic mutations can occur within their cells. Over time, a combination of inherited and lifestyle factors, including diet, smoking, and alcohol use, can contribute to the accumulation of genetic changes. Key genes involved in this process include oncogenes, tumor suppressor genes, and DNA repair genes. Mutations in these genes can disrupt normal cell growth and death, leading to the uncontrolled cell division characteristic of cancer.

3. Polyp to Cancer Transformation: Not all polyps will transform into cancer, and the process can take many years — often 10 to 15 years for a polyp to develop into full-blown cancer. However, the larger a polyp grows, and the more dysplastic its cells become, the greater the chance it will turn into cancer. Dysplasia refers to the abnormal appearance of cells, indicating a precancerous condition.

4. Invasion and Metastasis: Once cancer forms, it can grow into the wall of the colon or rectum, invading blood vessels or lymph nodes nearby. From there, cancer cells can break away and spread (metastasize) to other parts of the body, such as the liver or lungs, forming new tumors. This spread is what makes cancer, including colon cancer, so dangerous and potentially life-threatening.

Prevention and Early Detection: The gradual development process of colon cancer highlights the importance of regular screening, such as colonoscopies, which can identify and remove polyps before they turn into cancer. Understanding risk factors and making lifestyle changes can also reduce the likelihood of developing colon cancer.

Early detection of colon cancer, while it is still localized to the colon or at an early stage, significantly improves treatment outcomes. This is why awareness of the development process of colon cancer and participation in regular screening is vital for at-risk populations.

Signs and Symptoms of Colon and Rectal Cancer

Colon and rectal cancer (collectively known as colorectal cancer) often begins with little to no symptoms. As the cancer progresses, signs and symptoms become more noticeable and may vary depending on the cancer's location in the colon or rectum and the extent of its spread. Here are some common signs and symptoms associated with colorectal cancer:

Changes in Bowel Habits

• Persistent changes in bowel habits, including diarrhea, constipation, or a change in the consistency of your stool that lasts for more than a few days.
• A feeling that your bowel doesn't empty completely or the urge to have a bowel movement that doesn't relieve after going.

Blood in Stool

• Rectal bleeding with bright red blood.
• Blood in the stool, which might make it look dark brown or black, indicating that the bleeding might be happening higher up in the colon.

Abdominal Discomfort

• Abdominal pain, cramps, or gas discomfort that persists.
• Bloating or feeling full that does not improve.

Systemic Symptoms

• Unexplained weight loss without changes in diet or exercise habits.
• Fatigue or feeling unusually tired without obvious cause.
• Weakness or feeling light-headed.

Iron Deficiency Anemia

In some cases, colon or rectal cancer can cause bleeding that’s not visible, leading to anemia (a condition in which you lack enough healthy red blood cells to carry adequate oxygen to your body's tissues).

It's important to note that many of these symptoms can be caused by conditions other than colorectal cancer, such as infection, hemorrhoids, irritable bowel syndrome, or inflammatory bowel disease. However, if you experience any of these symptoms, especially if they persist or worsen, it's crucial to consult a healthcare provider for a thorough evaluation and appropriate diagnostic testing.

Early detection of colorectal cancer significantly improves the chance of successful treatment, making regular screenings vital, particularly for individuals over the age of 45 or those with a family history of the disease or other risk factors.

How colon and rectal cancer is diagnosed

Diagnosing colon and rectal cancer (colorectal cancer) involves a series of tests and procedures to confirm the presence of cancer and to determine its stage. Early detection is crucial for effective treatment and improved outcomes. Here’s how colorectal cancer is typically diagnosed:

1. Medical History and Physical Examination

The process begins with a thorough medical history to assess risk factors and symptoms. The doctor may perform a physical exam, including a digital rectal exam (DRE), to check for abnormalities or lumps in the rectum.

2. Fecal Occult Blood Test (FOBT) or Fecal Immunochemical Test (FIT)

These tests detect hidden blood in the stool, which can be an early sign of cancer. They are often used for screening purposes.

3. Colonoscopy

A colonoscopy is the most comprehensive diagnostic tool for colorectal cancer. A long, flexible tube equipped with a camera (colonoscope) is inserted into the rectum to examine the entire colon and rectum. If polyps or abnormalities are found, they can be removed or biopsied during the procedure.

4. Flexible Sigmoidoscopy

Similar to a colonoscopy, this procedure involves the use of a shorter tube to examine the lower part of the colon (sigmoid) and rectum. It's less invasive but does not allow the entire colon to be viewed.

5. Imaging Tests

Various imaging tests can help determine the extent (stage) of cancer and whether it has spread. These may include:

• Computed Tomography (CT) Scan: Creates detailed cross-sectional images of the body.
• Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues in the body.
• Ultrasound: Can be used, especially endorectal ultrasound, to assess how deeply rectal cancer has penetrated the wall of the rectum.
• Positron Emission Tomography (PET) Scan: Can help detect where cancer has spread.

6. Biopsy

A biopsy, often performed during a colonoscopy or sigmoidoscopy, involves taking a small sample of tissue from the polyp or suspicious area. This tissue is then examined under a microscope to look for cancer cells.

7. Blood Tests

While not diagnostic for colorectal cancer, blood tests can provide valuable information about the patient's overall health and how well their organs are functioning. A blood test for a substance called carcinoembryonic antigen (CEA) may be used to monitor treatment effectiveness and check for recurrence after treatment.

After the diagnosis, further tests may be conducted to determine the stage of cancer, which is crucial for planning the treatment. Early detection and timely treatment significantly improve the prognosis for colorectal cancer. Regular screenings are recommended for adults over the age of 45, or earlier for those with a family history or other risk factors.

Colon cancer treatments

Treatment for colon cancer is highly individualized and depends on the stage of the cancer, the location of the tumor, and the overall health of the patient. The main treatments for colon cancer include surgery, chemotherapy, radiation therapy, targeted therapy, and immunotherapy. Here’s an overview of these treatments:

1. Surgery

Surgery is often the primary treatment for early-stage colon cancer. The type of surgery performed depends on the stage and location of the cancer:

• Polypectomy: Removal of polyps during a colonoscopy, for very early cancer.
• Local excision: Removal of small, localized cancers that are on the surface of the colon lining.
• Partial colectomy: Removal of the part of the colon containing the cancer along with a margin of normal tissue on either side, and nearby lymph nodes. The remaining portions of the colon are then reconnected.
• Colostomy: For cancers that cannot be reconnected, an opening outside the body for waste to pass into a bag may be necessary, either temporarily or permanently.

2. Chemotherapy

Chemotherapy uses drugs to destroy cancer cells, usually by stopping the cancer cells' ability to grow and divide. It’s often used after surgery to eliminate any remaining cancer cells, in advanced cancer to shrink tumors and relieve symptoms, or to enhance the effectiveness of other treatments.

3. Radiation Therapy

Radiation therapy uses high-energy rays to target and destroy cancer cells. While less common for colon cancer than rectal cancer, it may be used to shrink a large tumor before surgery or to target cancer cells that remain after surgery.

4. Targeted Therapy

Targeted therapy drugs target specific abnormalities within cancer cells. By blocking these abnormalities, targeted drugs can cause cancer cells to die. It's mainly used for advanced colon cancer and often combined with chemotherapy.

5. Immunotherapy

Immunotherapy is a treatment that uses the body's immune system to fight cancer. It is more likely to be effective against colon cancers that have a high number of genetic changes, such as those with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR).

6. Palliative Care

In addition to treatments aimed at curing or controlling the disease, palliative care is important for relieving symptoms and side effects to improve the quality of life. Palliative care can be used while undergoing other aggressive treatments, such as surgery, chemotherapy, or radiation therapy.

The choice of treatment depends on several factors, and a multidisciplinary team of specialists will work together to determine the best approach for each individual patient. Regular follow-up is essential to monitor the patient's progress and manage any complications or signs of recurrence. Early detection and comprehensive treatment planning significantly improve the outcomes of colon cancer treatment.

Colon cancer prevention

Preventing colon cancer involves a combination of lifestyle changes and regular screenings. While not all colon cancers can be prevented, the following strategies can significantly reduce your risk:

Lifestyle Changes

• Eat a Healthy Diet: Emphasize fruits, vegetables, whole grains, and lean proteins. Reduce red meat consumption and avoid processed meats.
• Exercise Regularly: Aim for at least 30 minutes of moderate exercise on most days of the week.
• Maintain a Healthy Weight: Being overweight or obese increases your risk of colon cancer. Work towards achieving and maintaining a healthy weight.
• Limit Alcohol and Quit Smoking: Alcohol consumption and smoking are associated with an increased risk of colon cancer. Limit alcohol to no more than one drink a day for women and two for men, and avoid tobacco use.

Regular Screenings

Screening for colon cancer can help detect precancerous polyps so they can be removed before turning into cancer. Screening can also detect cancer at an early stage, when treatment is more likely to be successful. Recommendations for when to begin regular screenings vary, but generally start at age 45 for those at average risk. People with a family history of colon cancer or other risk factors may need to start screening earlier and/or be screened more frequently.

Genetic Testing and Counseling

For those with a family history of colon cancer, genetic testing and counseling can provide information about their risk and guide screening recommendations.

By adopting healthy lifestyle choices and undergoing regular screenings, individuals can significantly reduce their risk of developing colon cancer. Always consult with a healthcare provider to determine the most appropriate prevention and screening strategies for your individual risk factors and health status.