Colorectal Cancer: causes, risk factors, genetics, diagnoses, and treatments

Colorectal Cancer

  • Colorectal cancer is the third most common cancer diagnosed and the second cause of cancer death in both men and women in the United States.
  • People over 50 years of age and those with a family history of colorectal cancer are at an increased risk of developing the disease.
  • It is estimated that 1 in 22 men and 1 in 24 women will develop colorectal cancer.
  • Adenocarcinomas make up 95 percent of colorectal cancer cases.
  • Colorectal cancer is one of the more curable cancers when detected early, so it is important to get regular screening tests done.

 

Colorectal cancer arises in the inner lining of the large intestine. Colorectal cancer is the third most diagnosed cancer and second leading cancer death in the United States. On average, 1 in 22 men and 1 in 24 women will develop colorectal cancer in their lifetime. According to the American Cancer Society, there are expected to be approximately 50,000 deaths due to colorectal cancer this year. Colorectal cancer is one of the more curable cancers when detected early

 The Large Intestine and Colorectal Cancer

The large intestine is the long upside down u-shaped tubular tract located in the lower abdomen. This part of the digestive system is approximately five feet in length and consists of the cecum, the colon, and the rectum. The colon is made up of four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The colon’s primary function is to reclaim water and process waste products from the body and prepare stools for elimination; as stools move along the colon, it becomes more solid. The terminal portion of the colon is called the rectum, where stools are stored until they can be eliminated.

The lining of the colon and the rectum is a prime location for the development and growth of polyps. Polyps are abnormal tissue growths that look like small protrusions on the lining of the large intestine. Although unwanted, developing polyps in the colon are not uncommon. Most polyps are benign, meaning that they are noncancerous. However, since they are abnormal cell growth, some polyps may become malignant, or cancerous.

Colon cancer is often discussed together with rectal cancer, and together they are referred to as “colorectal cancer.” Colorectal cancer (CRC), which may also be called bowel cancer, may not be talked about as often as other cancers, but it is the third most common cancer and one of the leading causes of cancer deaths in the United States. It is for this very reason why it is important to stay on top of your colon and rectum health.

 How Frequent is Colorectal Cancer?

 

 

Colorectal cancer is the third most diagnosed cancer and second leading cancer death in the United States. On average, 1 in 22 men and 1 in 24 women will develop colorectal cancer in their lifetime. According to the American Cancer Society, there are expected to be approximately 50,000 deaths due to colorectal cancer this year. Fortunately, colorectal cancer survival rates have been steadily increasing through recent years due to early detections and with the rapid therapeutic advancement in the era of personalized medicine.

What Causes Colorectal Cancer?

            It is not known exactly what causes colorectal cancer, although a number of factors can increase your risk of developing the condition. These include:

Age – risk rises as you age, and in most cases are diagnosed in both men and women over 50 years of age.

Family history – having a family member who developed colorectal cancer may increase your risk of developing colorectal cancer. There is a significantly higher risk of developing the disease if a first-degree relative had colorectal cancer.

Ethnic group – colorectal cancer is present in all populations. However, it is more common among those with African or eastern European descent.

Medical conditions – inflammatory bowel diseases (IBDs), such as Crohn’s disease and ulcerative colitis, may increase your risk of developing colorectal cancer. Individuals with Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC), have a significantly increased risk of developing colorectal cancer. In fact, those with HNPCC could possibly even develop colorectal cancer before they are 50 years old. Familial adenomatous polyposis (FAP), a condition that causes individuals to develop hundreds of polyps in the lining of their colon and rectum, can also increase your risk of developing colorectal cancer. Studies have also shown that type 2 diabetes is linked to increased risk of developing colorectal cancer.

Body Mass Index – recent studies suggests that there may be a link between obesity and colorectal cancer. The higher an individual’s BMI is, the higher the risk of developing colorectal cancer.

 

Nutrition – research is ongoing into the links between diet and colorectal cancer. There is evidence that a diet high in fat and low in fiber is linked to an increased risk of developing colorectal cancer. Although data is not consistent, eating red meats or unprocessed meats may also increase your risk of developing the condition.

Tobacco and Alcohol – smoking tobacco increases your risk for colorectal cancer. Inhaling chemicals and toxins into the body damages DNA and mutates healthy cells, which could cause the development of precancerous polyps in the large intestine. Alcohol consumption may also affect an individual’s risk of developing colorectal cancer. Acetaldehyde is a known carcinogen and a product of alcohol metabolism that is more toxic than alcohol itself.

 

Symptoms of Colorectal Cancer

Individuals with colorectal cancer may experience the following signs and symptoms:

  • Persistent diarrhea or constipation
  • Change in stool consistency, such as narrow stools or black tar-like stools
  • Feeling that your bowel does not empty completely
  • Straining feeling in the rectum
  • Rectal bleeding or blood in the stool
  • Unexplained weight loss
  • Weakness or fatigue
  • Abdominal tenderness/discomfort such as cramps, gas, or pain

Symptoms will likely vary depending on the size and location of colorectal cancer. Many individuals with colorectal cancer experience no symptoms in the early stages of the condition. However, people can be diagnosed before they develop symptoms during a regular screening test, like a colonoscopy. These tests use special instruments to see inside your large intestine and look for any cancerous or pre-cancerous polyps.

 

Types of Colorectal Polyps and Adenocarcinoma

          Polyps are growths of excess tissue that often occur on the lining of the large intestine. They vary in size and may grow in two different shapes: flat (sessile) or mushroom-like (pedunculated). Sessile polyps lie flat against the mucous membrane of the large intestine, whereas pedunculated polyps attach to the lining of the large intestine by a long stalk. Polyps occur in about 20 to 30 percent of people over the age of 50 and tend to become more common as people age. The large majority of polyps are benign. However, there are certain types of polyps that may become cancerous if untreated.

The most common types of colorectal polyps include:

Inflammatory – this type of polyp is typically found in patients with an inflammatory bowel disease. Inflammatory polyps are generally benign and are unlikely to become malignant.

Hyperplastic – this type is relatively common and usually noncancerous. Although most colorectal cancers do not develop from hyperplastic polyps, the risk of developing the disease could increase if these polyps are untreated and continue to grow.

Adenomatous – also known as adenomas, this type of polyp is the most common. Approximately 70 percent of all polyps found in the large intestine are adenomatous polyps and are considered to be the clinically relevant precursors of colorectal cancer. If left untreated, this form of polyp may develop into an adenocarcinoma.

Colorectal adenocarcinomas are cancerous tumors which develop from the glandular tissues of the large intestine. Nearly 95 percent of colorectal cancers are from adenocarcinomas. The majority of colorectal cancers are adenocarcinomas because there are numerous glands within the lining of the large intestine. Other, less common types of colorectal cancers include lymphomas, sarcomas, gastrointestinal stromal tumors, and carcinoid tumors.

 

How to Diagnose Colorectal Cancer

Colorectal cancer may be suspected through the history of symptoms a patient presents. A careful and thorough physical examination by their physician may help determine whether a patient may have developed colorectal cancer. An endoscopic test, such as a colonoscopy, is usually the first test conducted in order to determine the diagnosis of colorectal cancer. With this form of screening, a small video camera attached to a thin, flexible tube, called a colonoscope, is inserted into the patient’s anus and into their large intestine. This allows the physician to look at the inside of the colon and rectum to screen for any polyps or tumors. When discovered, the polyps are removed and collected for biopsy. A biopsy is an examination of a sample of tissue to access if there are any abnormalities that are suggestive of a disease; in this case, colorectal cancer. Like most types of cancers, a biopsy is the most accurate method used by physicians to detect whether colorectal cancer is present. If malignancy has been detected, then the next step would be to grade and stage the cancer. The grade of colorectal cancer indicates the behavior of the cancer, whereas the stage refers to how extent the colorectal cancer is.  Identifying the cancer’s grade and stage allows medical professionals to develop optimal treatment plans for patients. Cancer cells must be observed under a microscope in order to identify their grade. To clearly demonstrate the cancer’s stage, lab tests, including blood work, and imaging tests, such as CT scans or ultrasounds are conducted.

 

Colorectal Cancer Grading and Staging

Cancer grading and staging take place after the initial diagnosis. The grade of colorectal cancer indicates how similar cancer cells look and act like normal cells. The grade gives the physician an idea of how the cancer may behave and what treatment would work best. A low-grade cancer is likely to be slower growing and less likely to spread than high-grade cancer.

The grades of colorectal cancer cells are as follows:

Grade 1 – “low grade;” cancer cells look like normal cells, and do not grow rapidly.

Grade 2 – cancer cells look similar to normal cells, but they grow much quicker than normal cells.

Grade 3 – “high grade;” cancers look abnormal and not like normal cells. In addition, they grow or spread more aggressively.

The stage refers to the extent of the cancer or how far it has spread. Staging colorectal cancer is essential to determine the most optimal treatment approach.

The stages of colorectal cancer are as follows:

Stage 0 – this is the earliest form of colorectal cancer. Stage 0 colorectal cancer is also called cancer in situ. There has not been any cancer growth beyond the innermost layer of the colon or rectum, called the mucosa.

Stage 1 – this stage indicates the cancer has grown through the mucosa, and into the next layer of the large intestine, called the submucosa. There are no cancer cells found in nearby tissue or lymph nodes.

Stage 2 – stage 2 colorectal cancer indicates that the disease has grown beyond the mucosa and submucosa. This stage of colorectal cancer is further classified as the following stages:

  • Stage 2A – the tumor has grown to the outer layers of the large intestine, but cancer has not spread to nearby tissues or lymph nodes.
  • Stage 2B – cancer has grown through the muscular layers of the large intestine and reached the membrane that holds the abdominal organs in place, known as the visceral peritoneum. However, no cancer cells are found in lymph nodes.
  • Stage 2C – the tumor has grown through the wall of the large intestine and to nearby organs. Cancer has not metastasized to the lymph nodes.

Stage 3 – this stage of colorectal cancer indicates that the disease has spread to the lymph nodes. Stage 3 can be further categorized as the following stages:

  • Stage 3A – cancer has grown through the inner lining or into the muscular layers of the large intestine. In addition, the disease is found in 1 to 3 nearby lymph nodes. The disease is not found in distant nodes or spread to other parts of the body.
  • Stage 3B – cancer has grown through into the outer lining of the large intestine, or into surrounding tissues or organs. Cancer cells are found in 1 to 3 nearby lymph nodes.
  • Stage 3C – cancer has grown through the inner lining or into the muscular layers of the large intestine and metastasized in 4 or more lymph nodes.

Stage 4 – stage 4 colorectal cancer indicates that the disease has metastasized to distant organs in the body. This stage is further classified as the following stages:

  • Stage 4A – cancer has spread to a single distant organ, such as the lungs or liver.
  • Stage 4B – cancer has reached two or more distant organs. Stage 4B colorectal cancer is the most advantaged stage of the disease.

 

How to Treat Colorectal Cancer

Treatment depends on the location of the cancer and how advanced or not the cancer is. Surgery, in most instances, is the first therapy patients will undergo in order to treat their colorectal cancer. Colorectal cancer may be treated with surgery alone, surgery and chemotherapy, and/or other treatments.

Surgery – Surgery is the most effective way to treat or cure colorectal cancer as it can successfully remove the cancer. Surgery alone is used when colorectal cancer is detected in the early stages. There are a variety of surgeries that can be employed. For low grade and early stages of colorectal cancer, cancerous growths may be removed endoscopically through a procedure called a polypectomy. Another common surgery for colorectal cancer is called a colectomy. This operation involves the removal of both the cancer and the surrounding tissue within the colon. If the cancer is located in the rectum, a proctectomy, which is an operation that removes the cancerous portion of the rectum, will be performed. Additional treatment typically is not needed after operations, unless the cancer is more advanced. When the cancer is at a more advanced stage, treatment involves a combination of surgeries and other therapies, such as chemotherapy and/or radiation therapy.

Chemotherapy/Radiation Therapy – Chemotherapy and/or radiation therapy are typically recommended for individuals who have a more advanced stage of colorectal cancer. These forms of treatment are usually followed by surgical removal of colorectal cancer. Chemotherapy is the use of drugs to help kill cancer cells, avoid recurrence of the disease, or prolong the life of the patient when surgery is not optional. Typically, chemotherapy is used for patients with cancer detected in the lymph nodes. Chemotherapy drugs may be administered orally in the form of a pill, or intravenously. The most common chemotherapy drugs used for colorectal cancer include 5-Fluorouracil, Irinotecan, and Oxaliplatin. In fact, several chemotherapy drugs are combined to treat most patients, as they have proved to function better together. Radiation therapy uses high-energy X-rays or particles to help destroy the DNA of cancerous cells, or help control the cancer in patients who do not qualify for surgery. Medical professionals tend not to use radiation therapy for the colon to avoid radiating the healthy small intestine, which can cause terrible side effects. Therefore, radiation therapy is typically used for patients with cancer located in the rectum where tumors tend to recur. Usually, radiation therapy is given in conjunction with chemotherapy, and this is called chemoradiation.

 

The Takeaway

Although it is the third most common cancer, colorectal cancer is one of the more curable cancers when detected early. As with most cancers, early detection is key. Regular screening tests should be done on patients who may be at increased risk, including people over the age of 50 or who have a family history of colorectal cancer. A colonoscopy is one of several measures that can be used for screening for colorectal cancer and should be repeated every ten years. It is the optimal test for examining the entire colon and both identifying and removing precancerous polyps. Untreated polyps may develop into adenocarcinomas, which is the most common type of colorectal cancer. If diagnosed with colorectal cancer, determining the stage of the cancer will affect your outlook. Patients diagnosed with early stages of colorectal cancer generally have the highest survival rate. However, treatments are available for all stages of colorectal cancer. Colorectal cancer is mainly treated and cured by surgery. However, depending on how advanced the cancer is, other therapies, such as chemotherapy and/or radiation therapy, may be used as an additive treatment.

 

The information in this document does not replace a medical consultation. It is for personal guidance use only. We recommend that patients ask their doctors about what tests or types of treatments are needed for their type and stage of the disease.

Sources:

  • American Cancer Society
  • The National Cancer Institute
  • National Comprehensive Cancer Network
  • American Academy of Gastroenterology
  • National Institute of Health
  • MD Anderson Cancer Center
  • Memorial Sloan Kettering Cancer Center

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