Introduction: When to Seek Diagnostic Testing

Rectal adenocarcinoma, commonly known as rectal cancer, is a serious condition that often develops slowly over many years. Understanding when to pursue diagnostic testing can make a significant difference in catching the disease early, when treatment options may be more effective.^[1]

You should consider seeking medical evaluation if you notice certain warning signs in your body. These symptoms don’t always mean you have rectal cancer, but they deserve attention from a healthcare professional. Common signs include blood in your stool, which may appear bright red or dark maroon in color. Changes in your bowel habits are also important to watch for, such as experiencing diarrhea or constipation more frequently than usual, or feeling that your bowel doesn’t empty completely after you use the bathroom.^[1]

Other symptoms that should prompt you to see a doctor include rectal bleeding, narrow or thin stools that look like a pencil, abdominal pain that doesn’t go away, unexplained weight loss, and persistent tiredness or weakness. Some people may also notice a lump in the rectum during self-examination or feel unusually fatigued.^[2]

Regular screening is particularly important for certain groups of people. If you have a first-degree relative (a parent, sibling, or child) who has been diagnosed with colon or rectal cancer, your risk increases significantly. People with a personal history of colon, rectal, or ovarian cancer should also be vigilant about screening. Additionally, if you’ve had high-risk adenomas – which are colorectal polyps that measure 1 centimeter or larger, or contain cells that look abnormal under a microscope – you need closer monitoring.^[4]

Inherited conditions also play a role in determining who should seek diagnostic testing. If you have genetic changes that increase your risk of familial adenomatous polyposis (FAP) or Lynch syndrome (also called hereditary nonpolyposis colorectal cancer), regular screening becomes even more critical. People with chronic inflammatory conditions like ulcerative colitis or Crohn disease, especially those who have had these conditions for eight years or more, face elevated risk as well.^[4]

Lifestyle factors can also influence your risk level. Smoking cigarettes, having obesity, consuming three or more alcoholic drinks per day, and being of Black race are all factors that increase the likelihood of developing rectal cancer. Age is another important consideration – the average age of diagnosis is 63, and the risk increases significantly as you get older.^[2]

Diagnostic Methods for Identifying Rectal Cancer

When rectal cancer is suspected, doctors use several different methods to confirm the diagnosis and understand the extent of the disease. The diagnostic process typically begins with a careful medical history and physical examination, followed by more specific tests.

Initial Examination

Your doctor will start by taking a detailed health history and performing a physical exam. This includes asking about your symptoms, how long you’ve had them, and whether you have any risk factors for rectal cancer. A crucial part of this initial assessment is the digital rectal exam (DRE), where the doctor inserts a lubricated, gloved finger into the lower part of your rectum to feel for lumps or anything unusual. While this may feel uncomfortable, it’s a quick and important examination that can detect abnormalities.^[6]

Endoscopic Examinations

The most important diagnostic tool for rectal cancer is colonoscopy, which allows doctors to look inside your rectum and colon. During this procedure, a long, flexible tube with a camera at the end, called a colonoscope, is gently inserted through the anus. The camera transmits images to a screen, allowing your doctor to examine the lining of your entire large intestine. You’ll receive medication before and during the procedure to keep you comfortable and relaxed.^[10]

If your doctor sees anything suspicious during the colonoscopy, they can take a small tissue sample right then and there. This procedure is called a biopsy, and it involves removing a tiny piece of tissue using special cutting tools passed through the colonoscope. The tissue sample is then sent to a laboratory where specialists examine it under a microscope to look for cancer cells.^[10]

An endoscopy examination with rigid sigmoidoscopy may also be performed. This is particularly important because it helps measure the exact distance from the tumor to the anal verge – the opening of the anus. This measurement, which must show the tumor is less than 15 centimeters from the anal verge to be classified as rectal cancer, influences treatment decisions.^[5]

Blood Tests

Several blood tests help doctors understand more about your condition. A complete blood count (CBC) reports the numbers of different types of cells in your blood. This test can reveal anemia, which may occur if the tumor has been bleeding. Blood tests can also check your liver and kidney function, which is important information before starting treatment.^[10]

A carcinoembryonic antigen (CEA) blood test may be ordered. CEA is a protein that’s sometimes elevated in people with colorectal cancer. While not everyone with rectal cancer has high CEA levels, if yours are elevated at diagnosis, this test can be useful for monitoring your response to treatment and watching for recurrence later on.^[2]

Imaging Tests

Once rectal cancer has been confirmed through biopsy, imaging tests help determine whether the cancer has spread beyond the rectum. These tests create detailed pictures of the inside of your body without requiring surgery.

Magnetic resonance imaging (MRI) scans use powerful magnets and radio waves to create detailed images of your rectum and surrounding tissues. An MRI is particularly good at showing how far the tumor has grown into the wall of the rectum and whether it has reached nearby lymph nodes or other structures. This information is critical for planning treatment.^[5]

Transrectal ultrasound is another imaging technique that can accurately determine local tumor extension and lymph node involvement. During this test, a small ultrasound probe is inserted into the rectum to create images using sound waves. This method is especially useful for examining tumors in the lower part of the rectum.^[5]

Computed tomography (CT) scans use X-rays taken from different angles to create cross-sectional images of your body. A baseline CT scan of your chest, abdomen, and pelvis helps doctors check whether the cancer has spread to other organs like the liver or lungs. You may need to drink a contrast liquid or receive an injection of contrast dye before the scan to make the images clearer.^[5]

Chest X-rays are simpler imaging tests that can show whether cancer has spread to the lungs. While not as detailed as CT scans, X-rays are quick and widely available.^[10]

Pathological Examination

After tissue is removed during biopsy, pathologists examine it closely in the laboratory. They look at the cells under a microscope to confirm whether cancer is present and to determine what type of cancer it is. Most rectal cancers are adenocarcinomas, which means they develop from gland-like cells in the lining of the rectum.^[7]

The pathologist’s report includes important details about the cancer cells, such as how abnormal they look compared to normal cells. This characteristic, called the grade of the cancer, helps predict how quickly the cancer might grow. The pathologist may also perform special tests on the tissue to look for specific genetic changes or proteins that could affect treatment decisions.^[10]

Additional Specialized Tests

All newly diagnosed patients with rectal cancer should be screened for something called DNA mismatch repair and microsatellite status. These genetic characteristics are present in up to 13 percent of all sporadic rectal cancer cases and can significantly influence treatment choices. Testing for these markers helps doctors understand whether your cancer might respond differently to certain treatments, including immunotherapy.^[5]

Diagnostic Testing for Clinical Trial Qualification

If you’re considering participating in a clinical trial for rectal cancer treatment, you may need to undergo additional or more specific diagnostic tests. Clinical trials are research studies that test new treatments, and they have strict requirements about who can participate. These requirements, called eligibility criteria, ensure patient safety and help researchers get accurate results.

Clinical trials typically require confirmation of your diagnosis through pathological examination of tissue samples. The pathology report must clearly document that you have rectal adenocarcinoma. Some trials may require the tissue to be reviewed by a specific pathologist associated with the study to ensure consistency in diagnosis across all participants.^[12]

Imaging tests are crucial for clinical trial enrollment because they help determine the stage of your cancer. The stage describes how large the tumor is, whether it has grown through the wall of the rectum, and whether it has spread to lymph nodes or distant organs. Different clinical trials accept patients at different stages of disease, so precise staging through MRI or CT scans is essential.^[12]

Blood tests are standard requirements for most clinical trials. Beyond the basic tests mentioned earlier, trials may require more detailed blood work to check specific organ functions. For example, liver function tests measure enzymes and proteins in your blood to ensure your liver is healthy enough for certain treatments. Kidney function tests do the same for your kidneys. Adequate blood cell counts are also important because many cancer treatments can affect your bone marrow’s ability to produce new blood cells.^[2]

Genetic and molecular testing of your tumor is increasingly important for clinical trial qualification. Many modern trials test targeted therapies or immunotherapies that work only on cancers with specific genetic characteristics. Your tumor tissue may be tested for mutations in genes like KRAS, NRAS, or BRAF, or for proteins like HER2. The presence or absence of these markers determines which trials you might be eligible for.^[2]

Some clinical trials require measurement of tumor markers in your blood. As mentioned earlier, CEA is a common tumor marker for colorectal cancer. Trials may want to know your baseline CEA level so they can track changes during treatment to see if the experimental therapy is working.^[2]

Your overall health status, often measured by something called performance status, must be evaluated for clinical trial participation. Performance status describes your ability to perform daily activities and take care of yourself. While not a laboratory test, this assessment is documented by your healthcare team and is an important qualification criterion. Most trials require participants to have good enough health to tolerate the experimental treatment.^[12]

Documentation of previous treatments is also required for clinical trial enrollment. If you’ve already received surgery, chemotherapy, or radiation therapy for your rectal cancer, the trial coordinators will need detailed records of what treatments you received, when you received them, and how you responded. Some trials are specifically designed for people who haven’t been treated yet, while others are for people whose cancer has progressed despite previous treatment.^[12]

Special imaging studies may be required depending on the clinical trial. For example, some trials use advanced imaging techniques like positron emission tomography (PET) scans to measure tumor metabolism and activity. PET scans can sometimes detect cancer that other imaging methods miss, and they can also help researchers measure how well a treatment is working by showing changes in tumor activity.^[2]

It’s important to understand that the specific diagnostic requirements vary significantly from one clinical trial to another. Each trial has its own protocol that lists exactly what tests and results are needed for enrollment. Working closely with your oncologist and the clinical trial team will help ensure you complete all necessary testing. They can explain which tests you need, why they’re required, and help coordinate the scheduling of these procedures.