The rectum is a 5 to 6 inch chamber that connects the colon to the anus. It is the job of the rectum to receive stool from the colon, to let you know that there is stool to be evacuated, and to hold the stool until defecation occurs. Rectal cancer is a disease in which malignant cells (cancer cells) form in the lining of the rectum. These cells may invade surrounding local tissues or may even spread throughout the body to other organs. Cancer is spread elsewhere in the body by invading the lymphatic and vascular systems. When the cancer spreads to lymph nodes or other organs, this is referred to as metastasis.
Symptoms of Rectal Cancer
The development of polyps of the colon or rectum commonly precedes the development of rectal cancer. Polyps are growths in the lining of the rectum. Polyps can be unrelated to cancer and are considered benign, pre-cancerous, or malignant. The best screening for rectal cancer is a colonoscopy. When a polyp is identified during a screening process, it is removed and sent to pathology for diagnosis. Symptoms of rectal cancer most often result from the local presence of the tumor and include:
- Rectal bleeding or bright red blood present with stool
- Change in bowel habits including constipation or diarrhea
- Narrowing of the stool, often called ribbon stools
- Sensation of incomplete evacuation
- Unexplained weight loss or change in appetite
- Abdominal distention, bloating, or the inability to have a bowel movement
- Pelvic pain
- Unexplained anemia
- Persistent chronic fatigue
A colonoscopy is a procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A routine colonoscopy screening often identifies an asymptomatic colon or rectal cancer, but is also performed when any of the above listed symptoms are present. A colonoscope is a thin flexible tube-like instrument with a light and small camera on the end that allows for visualization of inside the colon and rectum. It is during this process that a polyp may also be removed when identified.
A physical exam including a digital rectal exam may identify a tumor or blood in the stool. During a digital rectal exam, the doctor inserts a lubricated glove finger into the rectum to feel for any lumps or for anything that seems unusual. The physician is able to perform chemical testing of the stool called a fecal occult blood test to determine the presence of blood in the stool. Some medical conditions like bleeding hemorrhoids can also cause a false-positive test result.
An anoscopy can also be performed during a routine physical exam to assess for any rectal lesions, polyps or tumors. An anoscopy is an examination of the rectum using a small rigid tubular device also called an anal speculum that is inserted a few inches into the anus to evaluate problems of the anal canal.
A flexible sigmoidoscopy may also be utilized in diagnosing a rectal cancer. A flexible sigmoidoscopy is a thin small hollow fiber optic scope with a camera attached to the end of it that is introduced into the rectum and the lower third of the colon can be examined visibly by the doctor. The physician is able to visualize the lining of the rectum and if necessary a biopsy, which is removal of tissue, is able to be performed and the specimen sent for a diagnosis.
Staging of Rectal Cancer
Adenocarcinomas comprise the vast majority of colon and rectal cancers. However, there are other rare rectal cancers which in carcinoid, lymphoma, and sarcoma. Squamous cell carcinomas may develop in the transition area from the rectum to the anal verge and are considered anal carcinomas.
After a rectal cancer is diagnosed, diagnostic tests are performed to determine if the cancer cells have spread from within the rectum to other parts of the body. The process used to find out whether cancer has spread from within the rectum to other parts of the body is referred to as staging. The information gather through this process determines the stage of the disease. It is important to know the stage in order to develop a treatment plan. The following diagnostic studies may be used in the staging process:
- Chest x-ray: An x-ray of the organs inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.
- CT Scan (CAT Scan): A diagnostic study that creates a series of detailed pictures of the areas of the inside of the body, such as the chest, abdomen, and pelvis taken at angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or consumed orally to help the organs or tissue show up more clearly. This procedure may also be referred to as computed tomography, computerized tomography, or computerized axial tomography.
- MRI (magnetic resonance imaging): A diagnostic study that uses magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (MRI).
- PET scan (positron emission tomography scan): A diagnostic study used to find malignant tumor cells in the body. A small amount of radioactive glucose is injected into a vein. A PET scanner rotates around the body and makes a picture of where the glucose is being utilizes in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose that normal cells do.
- Endorectal ultrasound (ERUS): A diagnostic study in which a small transducer is directly inserted through the anus and into the rectum. The transducer bounces high-energy sound waves off the internal tissues or organs and makes echoes. The echoes detected are then converted by computer into an image that is displayed on a screen. An endorectal ultrasound is the most preferred method of staging both the depth of tumor penetration and local lymph node involvement.
- Carcinoembryonic antigen (CEA) assay: A blood test that measures the level of CEA in the blood. CEA is released into the bloodstream from both cancer cells and normal cells. When found in higher than normal amounts, it can be a sign of rectal cancer.
Stages of Rectal Cancer
Once the diagnosis of rectal cancer has been confirmed by biopsy and endorectal ultrasound, the clinical stage of the cancer is assigned. The treating physician uses staging to plan a specific treatment plan. Rectal cancer first invades locally and then progresses or spreads to regional lymph nodes and then to other organs of the body.
Rectal cancer is assigned stages I through IV, based on the following general criteria:
- Stage 0: Abnormal cells are found in the innermost lining of the rectum. Stage 0 is also called carcinoma in situ.
- Stage I: The tumor is confined to the lining of the rectum (the epithelium) or has not penetrated through the first layer of the muscle in the rectal wall.
- Stage II: The tumor has penetrated through to the outer wall of the rectum or has gone through it, possibly invading other local tissue or organs.
- Stage III: Any depth or size of tumor associated with regional lymph node involvement.
- Stage IV: Any of the previous criteria associated with distant metastasis.
When rectal cancer cannot be completely removed with surgery, a patient’s chance of cure is greatly diminished. Radiation and/or chemotherapy given prior to surgery are referred to as neoadjuvant therapy. Radiation therapy uses high energy x-rays or other types of radiation to kill cancer cells. External beam radiation uses a machine outside the body to send radiation toward the cancer.
Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping the cells from dividing. When chemotherapy is taken by mouth or injected into a vein, the drugs enter the bloodstream and can reach cancer cells throughout the body also referred to as systemic chemotherapy.
Neoadjuvant therapy can shrink rectal cancer and therefore allow complete surgical removal. This also allows for sphincter preserving surgery especially if the tumor is low lying in the rectum and enables the anus to be kept. Aggressive use of preoperative chemoradiation may allow for patients with larger low-lying rectal cancers to maintain anal function.
Adjuvant therapy is the goal of providing additional treatment after surgery and is used to reduce the risk of cancer recurrence by eliminating any remaining cancer. For patients who received neoadjuvant chemotherapy and radiation, additional chemotherapy is often given after surgery. If patients did not received neoadjuvant therapy, they may be treated with both chemotherapy and radiation therapy after surgery.
Surgical Treatment Options
Surgery, which involves removing the cancer, is the most common treatment for rectal cancer for all stages of the disease. The type of surgery used to remove the rectal cancer will depend on the location and size of the tumor, the stage of the cancer, and on the person’s general health.
- Polypectomy - If the rectal cancer is found at a very early stage, the surgeon may be able to remove it without cutting into the abdomen. If the cancer is found in a polyp, it can be removed under the visualization of a colonoscopy is called a polypectomy.
- Transanal Excision- Another option that can be performed without making an incision in the abdomen is a transanal excision. A transanal excision can be performed for small cancers that lie close, usually within two inches, of the anus. The operation involves cutting through all layers of the rectum to remove invasive cancer as well as some of the surrounding normal rectal tissue. This procedure is performed through the anus.
- Low Anterior Resection (LAR) - If the rectal cancer is located well above the anus, a low anterior resection can be performed. During the procedure, the entire rectal cancer, adjacent normal rectal tissue and surrounding lymph nodes are removed through an incision made in the lower abdomen. After the cancer is removed, the ends of the rectum are sewn back together. The passage of stool from the intestine through the anus is therefore preserved. If the cancer is lower in the rectum, the cut end of the large bowel may be attached directly to the anus, a procedure known as colo-anal anastomosis. When a colo-anal anastomosis is performed, some surgeons will create a temporary colostomy in order to protect the delicate surgical connection of the large intestine to the anus. After the patient has recovered from the surgery anywhere from four to eight weeks, the temporary colostomy is removed and the stool can again be passed through the anus.
- Abdominoperineal Resection (APR) - If the rectal cancer is located close to the anus, sometimes the anus must be removed with the cancer in an operation called an abdominoperineal resection. During an abdominoperineal resection, the entire rectal cancer, adjacent normal rectum, rectal sphincter or anus, and surrounding lymph nodes are removed through an incision in the lower abdomen and the perineum, which is the skin around the anus. Following the removal of the cancer, the incision in the perineum is sewn shut. The cut end of the large intestine is attached to an opening in the abdominal wall, called a colostomy. This opening is covered with a bag, which serves to collect stool as it passes through the large intestine and through the colostomy. In contrast to a low anterior resection, the colostomy is permanent. When the rectal cancer lies close to the sphincter or anus, an APR is typically recommended. In some situations, preoperative radiation therapy can be used to shrink the rectal cancer prior to surgery allowing for a sphincter sparing surgery and the patient is able to maintain control of bowel function.
- Laparoscopic Surgery- Laparoscopic surgery is used for many types of surgeries with the short term advantages of less pain, fewer wound complications, quicker post-operative recovery, and shorter hospital stays. Instead of making one long incision in the abdomen, the surgeon makes several smaller incisions. Special long instruments are inserted through these incisions to remove part of the rectum and lymph nodes. The surgeon is able to see inside the abdomen using one of the instruments with a small video camera on the end of it. Once the diseased part of the rectum has been freed, one of the incisions, usually in the mid-abdomen is made larger to allow for its removal. Laparoscopic-assisted surgery appears to be about as likely to be curative as the standard approach for stage I cancers.
Once a patient has been treated for rectal cancer, whether it be with radiation, chemotherapy, and/ or surgery, it is imperative to remain under surveillance for any recurrence of the rectal cancer. Procedures that are utilized in the surveillance process include follow up CT Scans, routine colonoscopies, and flexible sigmoidoscopies. Quite often flexible sigmoidoscopies may be performed every six months to on a yearly basis. Colonoscopies may be performed anywhere from a yearly basis to every three years. Once a patient has reached five years post rectal cancer, they are considered cured. However, routine colonoscopies are still performed to screen for other colon cancers not associated with the original rectal cancer.