Rectal cancer is cancer of the rectum, which is the final six inches of the digestive system. Waste matter from the colon is stored in the rectum until it is ready to be discharged from the anus.
Colon cancer and rectal cancer (often referred to under the umbrella term colorectal cancer) are very similar in their pathophysiology and in their signs and symptoms. The major difference between them is the anatomy of the rectum compared to the colon: The rectum is not completely surrounded by the same protective outer layer (called the serosa) as the colon, making it easier for a tumor to spread locally. For this reason, rectal cancer is much more likely than colon cancer to recur locally and may require different treatment options.
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Once you have been diagnosed with rectal cancer, one of the first things your doctor will want to do is determine what stage your cancer is at. This is important because the type of treatment that you receive depends on the cancer stage.
Although every patient’s cancer journey is unique, staging cancer gives an indication of your outlook and prognosis.
Staging is a system used to determine how advanced your rectal cancer is. It involves an assessment of whether the cancer is contained within the organ of origin (the rectum), whether it has spread to nearby lymph nodes and tissues, or if it has metastasized to other organs.
The TNM staging system is used in the United States to classify the stages of types of cancers, including colorectal cancers:
T – primary tumor. It describes the depth of invasion of the tumor into or beyond the wall of the rectum.
N – nodes. This describes whether cancer has spread to nearby lymph nodes and how many nodes are involved.
M – metastasis to other organs. This describes if rectal cancer has spread to any other organs and, if so, how many other organs are involved or if there are peritoneal metastases.
Each of the TNM stages can be broken down further and subclassified depending on the extent of the spread, either locally (within lymph nodes) or to other organs.
Another staging method is through the Prognostic Stage Groups devised by the American Joint Committee on Cancer (AJCC), which sets five stages of rectal cancer from stage 0 to stage IV. Stage 0 is where there is no spread beyond the rectal mucosa, while stage IV is where there is spread to one or more other sites or organs outside the rectum.
The two different staging systems can be confusing, especially if different healthcare providers use different systems to explain rectal cancer to you. This table has been modified from the American Cancer Society¹ and helps to simplify the overlap between the two systems:
When you are first diagnosed with rectal cancer, you will most likely have already met with your colorectal surgeon. If your colonoscopy/proctoscopy was performed by a gastroenterologist and not a colorectal surgeon, you may at this point be referred to a colorectal surgeon. You may also be referred to an oncologist, depending on the stage of your tumor.
In order to accurately determine the stage of your rectal cancer, you may need to undergo some or all of the following tests:
Colonoscopy or proctoscopy with biopsy
This procedure will need to be performed to give an initial diagnosis of rectal cancer. If the tumor has been removed during the colonoscopy/proctoscopy, it will be examined by a pathologist who will determine whether or not cancer has spread through the rectal wall.
The biopsy specimen can also be sent for gene testing and biomarking, which will help to determine your future risk of recurrence of colorectal cancer, as well as the most effective treatments for your specific cancer.
Final staging will be performed after surgery.
Computed tomography scanning (CT scanning)
CT scanning can show if cancer has spread through the full thickness of the rectum and if lymph nodes are involved. It can also look for spread to other organs, such as the lungs or liver. Sometimes, CT scanning is used to guide a needle biopsy of a mass in the lymph nodes, liver, lungs, or other organs to assess whether it is malignant.
Abdominal ultrasound can be used to identify tumors that may have spread to your liver, gallbladder, pancreas, or elsewhere in your abdomen. However, it can't look for tumors in the colon or rectum.
Endorectal ultrasound uses a special transducer that is inserted into the rectum. It is used to see how far through the rectal wall cancer has grown and whether it has reached nearby organs or lymph nodes.
Magnetic resonance imaging (MRI)
MRI can be used to identify whether a tumor has spread to other organs, especially the brain and spinal cord.
You may have a chest x-ray to see if the tumor has spread to the lungs, but this procedure has largely been replaced by CT scanning.
Positron emission tomography (PET) scanning
PET scanning can show collections of cancer cells, but it is not routinely used in rectal cancer staging.
Rectal cancer can have different signs and symptoms depending on its stage.
Very early-stage rectal cancer may be completely asymptomatic, which is why it is important to get screened if you are at high risk of developing rectal cancer or are over the age of 45.
Rectal cancer that is localized to the rectum could present with blood in your stool or a change in bowel pattern. Once the rectal cancer is larger, you could experience symptoms of lower abdominal pain, bloating, discomfort, or incomplete evacuation (the feeling that something remains behind after a bowel movement).
If your rectal cancer bleeds significantly, you may experience fatigue, and your doctor may diagnose anemia.
In late-stage rectal cancer, once the tumor has metastasized to other organs, you may experience symptoms related to the affected organs. For example, if cancer has spread to your liver, you may have a distended abdomen and jaundice (yellowing of the whites of the eyes). If it has spread to your lungs, you may experience shortness of breath.
Different stages of rectal cancer can require different treatments.
Surgery is typically the main treatment for rectal cancer. For early-stage cancer, your colorectal surgeon may be able to remove cancer completely through surgery alone.
For more advanced cancer, you may need chemotherapy or radiation therapy as well as surgery. Sometimes in cases where the tumor is too large to be removed surgically, it may be necessary to undergo radiation therapy to shrink the tumor before it is removed through surgery.
If your tumor is small enough to be completely surgically removed but has already spread to other organs, you may need ablation or embolization therapy along with your surgery. This technique is used to “kill off” small tumors that have spread to other organs by eliminating their blood supply.
Radiation therapy is often used to treat rectal cancer. If it is used in conjunction with chemotherapy, it is called chemoradiation. Radiation therapy may be used to decrease the size of your rectal tumor, making it easier to remove surgically. You may also require radiation therapy after surgery if there are remaining cancer cells or cancer has spread to lymph nodes. Very late-stage cancer may require radiation therapy to alleviate the symptoms that the cancer is causing.
Chemotherapy can be used to help treat rectal cancer of different stages. In the early stages, you may require chemotherapy after surgery to ensure that any cancer cells that may have been left behind during surgery are killed off. In more advanced stages, chemotherapy can be used to shrink rectal cancers before surgery or to alleviate the symptoms of metastases.
Cancer survival is often measured in terms of five-year survival. This table² indicates five-year survival rates for rectal cancer.
Note that this table gives an indication only. Every patient has their own cancer journey that is unique to their circumstances.
Determining the stage of your rectal cancer is important because it factors in your treatment plan and overall outlook.
Generally, the more advanced the tumor, the higher the TNM score.
Rectal cancer is staged using various diagnostic tools, including surgery, biopsy, CT scanning, ultrasound, and MRI scanning.
Treatment depends on the stage of your rectal cancer. If your rectal cancer is localized, you may only require surgery to remove it. If your cancer is more advanced and has spread locally or other organs, you may need surgery as well as chemoradiation.
Generally, the lower the stage of your tumor when you are diagnosed with rectal cancer, the better your prognosis. This is why it is so important to have regular screenings and see your doctor if you have any symptoms of rectal cancer.