What is cancer of the colon and rectum?

Colon cancer is cancer of the large intestine (colon), the lower part of your digestive system. Rectal cancer is cancer of the last several inches of the colon. Together, they’re often referred to as colorectal cancers. Most cases of colon cancer begin as small, noncancerous (benign) clumps of cells called adenomatous polyps.

Symptoms

Signs and symptoms of colon cancer include:

  • A change in your bowel habits, including diarrhoea or constipation or a change in the consistency of your stool, that lasts longer than four weeks
  • Rectal bleeding or blood in your stool
  • Persistent abdominal discomfort, such as cramps, gas or pain
  • A feeling that your bowel doesn’t empty completely
  • Weakness or fatigue
  • Unexplained weight loss

Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they’ll likely vary, depending on the cancer’s size and location in your large intestine.

Causes

In most cases, it’s not clear what causes colon cancer. Doctors know that colon cancer occurs when healthy cells in the colon develop errors in their DNA. Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell’s DNA is damaged and becomes cancerous, cells continue to divide — even when new cells aren’t needed. As the cells accumulate, they form a tumour. With time, the cancer cells can grow to invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body.

Inherited gene mutations that increase the risk of colon cancer

Inherited gene mutations that increase the risk of colon cancer can be passed through families, but these inherited genes are linked to only a small percentage of colon cancers. Inherited gene mutations don’t make cancer inevitable, but they can increase an individual’s risk of cancer significantly.

The most common forms of inherited colon cancer syndromes are:

  • Hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC, also called Lynch syndrome, increases the risk of colon cancer and other cancers. People with HNPCC tend to develop colon cancer before age 50
  • Familial adenomatous polyposis (FAP). FAP is a rare disorder that causes you to develop hundreds to  thousands of polyps in the lining of your colon and rectum. People with untreated FAP have a greatly increased risk of developing colon cancer before age 40

FAP, HNPCC and other, rarer inherited colon cancer syndromes can be detected through genetic testing. If you’re concerned about your family’s history of colon cancer, talk to your doctor about whether your family history suggests you have a risk of these conditions.

Association between diet and increased colon cancer risk

Studies of large groups of people have shown an association between a typical Western diet and an increased risk of colon cancer. It’s not clear why this occurs, but researchers are studying whether a high-fat, low-fibre diet affects the microbes that live in the colon or causes underlying inflammation that may contribute to cancer risk.

Treatment

The type of treatment your doctor recommends will depend largely on the stage of your cancer. The three primary treatment options are surgery, chemotherapy and radiation.

Surgery for early-stage colon cancer

If your colon cancer is very small, your doctor may recommend a minimally invasive approach to surgery, such as:

  • Removing polyps during colonoscopy. If your cancer is small, localised in a polyp and in a very early stage, your doctor may be able to remove it completely during a colonoscopy
  • Endoscopic mucosal resection. Removing larger polyps may require also taking a small amount of the lining of the colon in a procedure called endoscopic mucosal resection
  • Minimally invasive surgery. Polyps that can’t be removed during colonoscopy may be removed using laparoscopic surgery. In this procedure, your surgeon performs the operation through several small incisions in your abdominal wall, inserting instruments with attached cameras that display your colon on a video monitor. The surgeon may also take samples from lymph nodes in the area where the cancer is located

Surgery for invasive colon cancer

If your colon cancer has grown into or through your colon, your surgeon may recommend:

  • Partial colectomy. During this procedure, the surgeon removes the part of your colon that contains the cancer, along with a margin of normal tissue on either side of the cancer. Your surgeon is often able to reconnect the healthy portions of your colon or rectum
  • Surgery to create a way for waste to leave your body. When it’s not possible to reconnect the healthy portions of your colon or rectum, you may need to have a permanent or temporary colostomy. This involves creating an opening in the wall of your abdomen from a portion of the remaining bowel for the elimination of body waste into a special bag. Sometimes the colostomy is only temporary, allowing your colon or rectum time to heal after surgery. In some cases, however, the colostomy may be permanent
  • Lymph node removal. Nearby lymph nodes are usually also removed during colon cancer surgery and tested for cancer

Surgery for advanced cancer

If your cancer is very advanced or your overall health very poor, your surgeon may recommend an operation to relieve a blockage of your colon or other conditions in order to improve your symptoms. This surgery isn’t done to cure cancer, but instead to relieve signs and symptoms, such as bleeding and pain.

In specific cases where the cancer has spread only to the liver and if your overall health is otherwise good, your doctor may recommend surgery to remove the cancerous lesion from your liver. Chemotherapy may be used before or after this type of surgery. This treatment may improve your prognosis.

Chemotherapy

Chemotherapy for colon cancer is usually given after surgery if the cancer has spread to the lymph nodes. In this way, chemotherapy may help reduce the risk of cancer recurrence. Chemotherapy may be used before surgery to shrink the cancer before an operation.

Chemotherapy can also be given to relieve symptoms of colon cancer that has spread to other areas of the body. In people with rectal cancer, chemotherapy is typically used along with radiation therapy. This combination is often used before and after surgery.

Radiation therapy

Radiation therapy is rarely used in early-stage colon cancer, but is a routine part of treating rectal cancer, especially if the cancer has penetrated through the wall of the rectum or travelled to nearby lymph nodes. Radiation therapy, usually combined with chemotherapy, may be used before surgery in order to make the operation easier and to reduce the chance that an ostomy will be necessary. It can also be used after surgery to reduce the risk that the cancer may recur in the area of the rectum where it began.