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Cancer of the colon or rectum is also called colorectal cancer. In the United States, colorectal cancer is the fourth most common cancer in men, after skin, prostate, and lung cancer. It is also the fourth most common cancer in women, after skin, lung, and breast cancer.
Diagram shows the colon and rectum. Image courtesy of NCI.
The Colon and Rectum
The colon and rectum are parts of the digestive system. They form a long, muscular tube called the large intestine (also called the large bowel). The colon is the first 4 to 5 feet of the large intestine, and the rectum is the last 4 to 5 inches. The part of the colon that joins to the rectum is the sigmoid colon. The part that joins to the small intestine is the cecum.
Partly digested food enters the colon from the small intestine. The colon removes water and nutrients from the food and stores the rest as waste. The waste passes from the colon into the rectum and then out of the body through the anus.
Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body. Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place. Sometimes this orderly process goes wrong. New cells form when the body does not need them, and cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor. Tumors can be benign or malignant:
- Benign tumors are not cancer:
- Benign tumors are rarely life-threatening.
- Generally, benign tumors can be removed, and they usually do not grow back.
- Cells from benign tumors do not invade the tissues around them.
- Cells from benign tumors do not spread to other parts of the body.
- Malignant tumors are cancer:
- Malignant tumors are generally more serious than benign tumors. They may be life-threatening.
- Malignant tumors usually can be removed, but sometimes they grow back.
- Cells from malignant tumors can invade and damage nearby tissues and organs.
- Cells from malignant tumors can spread to other parts of the body. The cells spread by breaking away from the original cancer (primary tumor) and entering the bloodstream or lymphatic system. They invade other organs, forming new tumors and damaging these organs. The spread of cancer is called metastasis.
Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer. Cancers affecting either of these organs may also be called colorectal cancer.
When colorectal cancer spreads outside the colon or rectum, cancer cells are often found in nearby lymph nodes. If cancer cells have reached these nodes, they may also have spread to other lymph nodes, the liver, or other organs.
When cancer spreads (metastasizes) from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if colorectal cancer spreads to the liver, the cancer cells in the liver are actually colorectal cancer cells. The disease is metastatic colorectal cancer, not liver cancer. It is treated as colorectal cancer, not liver cancer. Doctors sometimes call the new tumor "distant" or metastatic disease.
No one knows the exact causes of colorectal cancer. Doctors can seldom explain why one person develops the disease and another does not. However, it is clear that colorectal cancer is not contagious. No one can "catch" this disease from another person.
Research has shown that people with certain risk factors are more likely than others to develop colorectal cancer. A risk factor is anything that is linked to an increased chance of developing a disease. Studies have found the following risk factors for colorectal cancer:
Colon polyps. Image courtesy of NCI.
- Age » Colorectal cancer is more likely to occur as people get older. More than 90 percent of people with this disease are diagnosed after age 50. The average age at diagnosis is in the mid-60s.
- Colorectal polyps » Polyps are growths on the inner wall of the colon or rectum. They are common in people over age 50. Most polyps are benign (noncancerous), but some polyps (adenomas) can become cancer. Finding and removing polyps may reduce the risk of colorectal cancer.
- Family history of colorectal cancer » Close relatives (parents, brothers, sisters, or children) of a person with a history of colorectal cancer are somewhat more likely to develop this disease themselves, especially if the relative had the cancer at a young age. If many close relatives have a history of colorectal cancer, the risk is even greater.
- Genetic alterations » Changes in certain genes increase the risk of colorectal cancer.
- Personal history of colorectal cancer » A person who has already had colorectal cancer may develop colorectal cancer a second time. Also, women with a history of cancer of the ovary, uterus (endometrium), or breast are at a somewhat higher risk of developing colorectal cancer.
- Ulcerative colitis or Crohn's disease » A person who has had a condition that causes inflammation of the colon (such as ulcerative colitis or Crohn's disease) for many years is at increased risk of developing colorectal cancer.
- Diet » Studies suggest that diets high in fat (especially animal fat) and low in calcium, folate, and fiber may increase the risk of colorectal cancer. Also, some studies suggest that people who eat a diet very low in fruits and vegetables may have a higher risk of colorectal cancer. More research is needed to better understand how diet affects the risk of colorectal cancer.
- Cigarette smoking » A person who smokes cigarettes may be at increased risk of developing polyps and colorectal cancer.
Screening for cancer before a person has symptoms can help the doctor find polyps or cancer early. Finding and removing polyps may prevent colorectal cancer. Also, treatment for colorectal cancer is more likely to be effective when the disease is found early. To find polyps or early colorectal cancer:
- People in their 50s and older should be screened.
- People who are at higher-than-average risk of colorectal cancer should talk with their doctor about whether to have screening tests before age 50, what tests to have, the benefits and risks of each test, and how often to schedule appointments.
Common symptoms of colorectal cancer include:
- A change in bowel habits
- Diarrhea, constipation, or feeling that the bowel does not empty completely
- Blood (either bright red or very dark) in the stool
- Stools that are narrower than usual
- General abdominal discomfort (frequent gas pains, bloating, fullness, and/or cramps)
- Weight loss with no known reason
- Constant tiredness
- Nausea and vomiting
Most often, these symptoms are not due to cancer. Other health problems can cause the same symptoms. Anyone with these symptoms should see a doctor so that any problem can be diagnosed and treated as early as possible. Usually, early cancer does not cause pain. It is important not to wait to feel pain before seeing a doctor.
If the biopsy shows that cancer is present, the doctor needs to know the extent (stage) of the disease to plan the best treatment. The stage is based on whether the tumor has invaded nearby tissues, whether the cancer has spread and, if so, to what parts of the body. Doctors describe colorectal cancer by the following stages:
- Stage 0 » The cancer is found only in the innermost lining of the colon or rectum. Carcinoma in situ is another name for Stage 0 colorectal cancer.
- Stage I » The cancer has grown into the inner wall of the colon or rectum. The tumor has not reached the outer wall of the colon or extended outside the colon. Dukes' A is another name for Stage I colorectal cancer.
- Stage II » The tumor extends more deeply into or through the wall of the colon or rectum. It may have invaded nearby tissue, but cancer cells have not spread to the lymph nodes. Dukes' B is another name for Stage II colorectal cancer.
- Stage III » The cancer has spread to nearby lymph nodes, but not to other parts of the body. Dukes' C is another name for Stage III colorectal cancer.
- Stage IV » The cancer has spread to other parts of the body, such as the liver or lungs. Dukes' D is another name for Stage IV colorectal cancer.
- Recurrent cancer » This is cancer that has been treated and has returned after a period of time when the cancer could not be detected. The disease may return in the colon or rectum, or in another part of the body.
Colon cancer staging; shows tumors growing through layers of the colon wall for Stage 0, Stage I, Stage II, Stage III, and Stage IV colon cancer. Inset shows serosa, muscle, submucosa and mucosa layers of the colon wall, and lymph nodes and blood vessels. Image courtesy of NCI.
Treatment for colorectal cancer may involve surgery, radiation therapy, or chemotherapy. Some people have a combination of treatments. Colon cancer sometimes is treated differently from rectal cancer.
Surgery is the most common treatment for colorectal cancer. It is a type of local therapy. It treats the cancer in the colon or rectum and the area close to the tumor.
A small malignant polyp may be removed from the colon or upper rectum with a colonoscope. Some small tumors in the lower rectum can be removed through the anus without a colonoscope. For a larger cancer, the surgeon makes an incision into the abdomen to remove the tumor and part of the healthy colon or rectum. Some nearby lymph nodes also may be removed. The surgeon checks the rest of the intestine and the liver to see if the cancer has spread.
When a section of the colon or rectum is removed, the surgeon can usually reconnect the healthy parts. However, sometimes reconnection is not possible. In this case, the surgeon creates a new path for waste to leave the body. The surgeon makes an opening (a stoma) in the wall of the abdomen, connects the upper end of the intestine to the stoma, and closes the other end. The operation to create the stoma is called a colostomy. A flat bag fits over the stoma to collect waste, and a special adhesive holds it in place.
For most people who have a colostomy, it is temporary. It is needed only until the colon or rectum heals from surgery. After healing takes place, the surgeon reconnects the parts of the intestine and closes the stoma. Some people, especially those with a tumor in the lower rectum, need a permanent colostomy.
Chemotherapy uses anticancer drugs to kill cancer cells. It is called systemic therapy because it enters the bloodstream and can affect cancer cells throughout the body.
The patient may have chemotherapy alone or combined with surgery, radiation therapy, or both. Chemotherapy given before surgery is called neoadjuvant therapy. Chemotherapy before surgery may shrink a large tumor.
Chemotherapy after surgery is called adjuvant therapy. Adjuvant therapy is used to destroy any remaining cancer cells and prevent the cancer from coming back in the colon or rectum, or elsewhere.
Chemotherapy is also used to treat people with advanced disease. Anticancer drugs are usually given through a vein, but some also may be given by mouth. The patient may be treated in an outpatient part of the hospital, at the doctor's office, or at home. Rarely, a hospital stay may be needed.
Radiation therapy (also called radiotherapy) is local therapy. It uses high-energy rays to kill cancer cells. It affects cancer cells only in the treated area. Doctors use two types of radiation therapy to treat cancer. Sometimes people receive both types:
- External radiation » The radiation comes from a machine. Most patients go to the hospital or clinic for their treatment, generally 5 days a week for several weeks. In some cases, external radiation is given during surgery.
- Internal radiation (implant radiation) » The radiation comes from radioactive material placed in thin tubes put directly into or near the tumor. The patient stays in the hospital, and the implants generally remain in place for several days. Usually they are removed before the patient goes home.
Source: National Cancer Institute
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