Colorectal cancer is a cancer that starts in the colon or the rectum. This cancer can also be named colon cancer or rectal cancer, depending on the part of the intestine where the cancer begins. Colon cancer and rectal cancer are often grouped due to their common and similar features.

Colon cancer typically affects older adults, though it can happen at any age. It usually begins as small, noncancerous (benign) clumps of cells called polyps that form on the inside of the colon.

Colorectal Cancer in Nigeria

In Nigeria today, colorectal cancer is the most common type of gastrointestinal cancer in Nigeria. It was rare among Nigerians in the 1960s, but at the moment, it seems to be increasing in incidence and rapidly growing. The increasing occurrence of colorectal cancer in Nigeria has been linked to both environmental and hereditary factors, with environmental factors playing a more significant role in Nigeria, due to economic development and changes in dietary and lifestyle preferences.

Presently, colorectal cancer has moved from being the 10^th most common cancer to the 4^th most common cancer in adults after breast, cervical, and prostate cancers. The incidence rate of this cancer in Nigeria is 3.4 cases per 100,000. Even with the incidence rate of colorectal cancer high in the country, it is still about one-tenth of what is seen in developed countries e.g. State of Connecticut in the USA has an incidence rate of 3.5 cases per 100,000.

Prognosis

For every colorectal cancer patient irrespective of its stage, the five-year relative survival rate is 64.4%. This means, that for every 100 people diagnosed with colorectal cancer, 64 out of them are expected to be alive after five years of diagnosis.

The survival rate is encouragingly high at 92% if the cancer was diagnosed earlier, with treatment commencing at its earliest stage.

The survival rates for more advanced stages have been steadily increasing as well, due primarily to the availability of more effective treatment options and an increasingly better understanding of the disease as time goes on.

Signs and Symptoms of Colorectal Cancer

Colorectal cancer-related symptoms are numerous and nonspecific. It may not present any symptoms, especially in the early stages. It can be present for several years before symptoms develop. If individuals do experience symptoms during the early stages, they may include:

• Constipation
• Diarrhea
• Changes in stool color
• Changes in stool shape, such as narrowed stool
• Blood in the stool
• Bleeding from the rectum
• Excessive gas
• Abdominal cramps
• Abdominal pain
• Excessive fatigue
• Unexplained weakness
• Unintentional weight loss
• Changes in one’s stool that last longer than a month
• Feeling like one’s bowels don’t empty
• Vomiting

If colon cancer spreads to other parts of the body, an individual may also experience:

• Jaundice (yellow eyes and skin)
• Swelling in hands or feet
• Breathing difficulties
• Chronic headaches
• Blurry vision
• Bone fractures

What are the Causes of Colorectal Cancer?

The main cause of colorectal cancer is relatively unknown, but certain factors can increase an individual’s risk of colorectal cancer.

1. Unavoidable Factors

Some factors that increase the risk of developing colorectal cancer are unavoidable and cannot be changed.

• Age: This risk of colorectal cancer increases as an individual gets older, it can be diagnosed at any age, but most individuals with colon cancer are older than 50 years. For colon cancer, the average age at the time of diagnosis for men is 68 years, and for women 72 years. For rectal cancer, it is age 63 for both men and women.
• Race and Ethnic Background: Jews and Blacks i.e., (African Americans and Africans) are more vulnerable to colorectal cancer.
• Personal History of Colorectal Cancer of Colorectal Polyps: If an individual has already had colorectal cancer or noncancerous colon polyps, even if it was completely removed; he/she is more likely to develop cancer in other parts of the colon and rectum in the future.
• Family History of Colon Cancer: Individuals who have a family history of colorectal cancer especially from first–degree relatives (i.e. parents, brothers, sisters, grandparents, etc.), have a risk of developing colorectal cancer shortly. The risk further increases if other close relatives have also developed colorectal cancer or if a first-degree relative was diagnosed at a younger age.
• Rare Inherited Conditions:Some gene mutations passed through generations of an individual’s family can increase the risk of colon cancer significantly. Only a small percentage of colon cancers are linked to inherited genes.
• Inflammatory Bowel Conditions:Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease can increase the risk of colon cancer.
• Adenomatous Polyps (Adenomas).Polyps are not cancer, but some types of polyps called adenomas can develop into colorectal cancer over time. Polyps removal can prevent colorectal cancer. People who have had adenomas have a greater risk of additional polyps and colorectal cancer, and they should have follow-up screening tests regularly.

2. Avoidable Factors

Here, an individual decreases the risk of developing colorectal cancer. Many lifestyle-related factors have been linked to colorectal cancer. The links between diet, weight, and exercise and colorectal cancer risk are some of the strongest for any type of cancer. Avoidable risk factors include:

• Obesity (Being Overweight): People who are obese have an increased risk of colon cancer and an increased risk of dying of colorectal cancer when compared with people considered normal weight. Being overweight (especially having a larger waistline) raises the risk of colon and rectal cancer in both men and women, but the link seems to be stronger in men.
• Physical Inactivity: Inactive people (who don’t exercise) are more likely to develop colorectal cancer. Involving in regular physical activities may reduce the risk of colorectal cancer.
• Certain Types of Diets: Diets that are high in red meats i.e. beef, pork, lamb, and processed meats like hotdogs can raise the risk of colorectal cancer.
• Smoking: People who smoke are more likely to develop and die from colorectal cancer, especially since smoking is known to be the main cause of lung cancer.
• Alcohol: People who tend to drink alcohol moderately or heavily tend to develop colorectal cancer.
• Type 2 Diabetes Patients: Individuals with type 2 diabetes or insulin resistance have an increased risk of colon cancer. Both type 2 diabetes and colorectal cancer share some of the same risk factors (such as being overweight and physical inactivity), yet they have a higher and increased risk.

Prevention of Colorectal Cancer

Certain risk factors for colorectal cancer, such as family history and age, aren’t preventable. However, lifestyle factors that may contribute to colorectal cancer are preventable and may help reduce the overall risk of developing this disease.

• Colorectal Cancer Screening can help to discover colorectal cancer in individuals with no symptoms of the disease. Regularly going for colorectal screening is the best way of preventing colorectal cancer.
• The use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs)
• Limiting red and processed meats and eating more vegetables and fruits may help lower the risk of colorectal cancer. Also, the use of vitamin D and calcium supplements can help lower the risk of colorectal cancer.
• Excessive alcohol intake has been known to be a risk factor for colorectal cancer; limiting the intake of alcohol can help to reduce the risk of colorectal cancer in any individual.
• Quitting smoking may help lower the risk of colorectal cancer.
• Keeping fit and getting involved in physical activity can help to lower the risk of colorectal cancer.
• Individuals with a family history of obesity need to maintain a healthy weight i.e. work to maintain their weight. There should be an aim to lose weight slowly by increasing the amount of exercise one gets and reducing the number of calories one eats.

Diagnosis of Colorectal Cancer

It is recommended that healthy individuals get screened even when they show no sign or symptom of colorectal cancer to detect colorectal cancer especially once they reach the age of 50 years. This test would also help to learn if cancer might have spread to another part of the part from its origin.

In addition to a physical examination, the following tests may be used to diagnose colorectal cancer.

• Colonoscopy: This test allows the entire rectum and colon using a long, flexible, and slender tube attached to a video camera and monitor to be checked while the patient is sedated. Once the colorectal cancer is found, a complete diagnosis is made, and the tumor is removed through surgery.
• Biopsy: This test can best determine the presence of colorectal cancer.
• Computed Tomography (CT or CAT) Scan: A CT scan can be used to measure the tumor’s size. In a person with colorectal cancer, a CT scan can check for the spread of cancer to the lungs, liver, and other organs. It is often done before surgery.
• Chest X-ray: An x-ray may be done after colorectal cancer has been diagnosed to see if the cancer has spread to the lungs.
• Angiography: Angiography is an x-ray test for looking at blood vessels. If the cancer has spread to the liver, this test can show the arteries that supply blood to those tumors.
• Ultrasound
• Magnetic Resonance Imaging (MRI) Scan
• Positron Emission Tomography (PET) Scan

Treatment of Colorectal Cancer

Treatment options for colorectal cancer include:

Surgery: In a situation where the tumour is very small, a doctor may recommend a minimal form of surgery, such as:

• Polypectomy: Here the doctor removes the polyps during the early stage of the colorectal cancer. This is usually done during colonoscopy.
• Endoscopic Mucosal Resection: This is removing larger polyps during colonoscopy using special tools to remove the polyp and a small amount of the inner lining of the colon.
• Minimally Invasive Surgery (Laparoscopic Surgery).Polyps that cannot be removed during a colonoscopy may be removed using laparoscopic surgery. Here, the surgeon operates through several small incisions in the abdominal wall, inserting instruments with attached cameras that display the colon on a video monitor.

But in certain situations when the cancer has grown into or through the colon, a doctor may recommend:

• Partial Colectomy: During this procedure, the doctor (surgeon) advises the removal of some part of the colon that contains the cancer, along with a margin of normal tissue on either side of the cancer. The surgeon is often able to reconnect the healthy portions of the colon or rectum. This procedure can commonly be done by a minimally invasive approach (laparoscopy).
• Lymph Node Removal: Nearby lymph nodes are usually also removed during colon cancer surgery and tested for cancer.
• Ostomy: Once it becomes impossible to reconnect the healthy portions of the colon or rectum, Ostomy is recommended. This involves creating an opening in the wall of the abdomen from a portion of the remaining bowel for the elimination of stool into a bag that fits securely over the opening. Sometimes the ostomy is only temporary, allowing the colon or rectum time to heal after surgery. In some cases, however, the colostomy may be permanent.

Chemotherapy: This is the use of drugs to destroy cancer cells. It is usually given after surgery if the cancer is larger or has spread to the lymph nodes. It might also be used before an operation to shrink a large cancer so that it is easier to remove with surgery. It can also be used to relieve symptoms of colon cancer that cannot be removed with surgery or that have spread to other areas of the body. Sometimes it is combined with radiation therapy.

Radiation Therapy: Using powerful energy sources, such as X-rays and protons, to kill cancer cells, radiation therapy can be used to shrink a large cancer before an operation so that it can be removed more easily. But when surgery is not an option, radiation therapy might be used to relieve symptoms, such as pain. Sometimes radiation is combined with chemotherapy.

Targeted Drug Therapy: Targeted drug treatments focus on specific abnormalities present within cancer cells. By blocking these abnormalities, targeted drug treatments can cause cancer cells to die. It is usually combined with chemotherapy. Targeted drugs are typically reserved for people with advanced colon cancer.

Immunotherapy: This is a drug treatment that uses the immune system to fight cancer. The body's disease-fighting immune system may not attack the cancer because the cancer cells produce proteins that blind the immune system cells from recognizing the cancer cells. Immunotherapy works by interfering with that process. It is usually reserved for advanced colon cancer.