Symptoms and Diagnostic Methods of Colorectal Cancer

< Common Symptoms of Colorectal Cancer >

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• In the early stages of colorectal cancer, there are usually no symptoms, and by the time symptoms appear, the disease is often already quite advanced. Below are the main symptoms of colorectal cancer.

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• Changes in bowel habits, such as suddenly having difficulty passing stool or changes in the frequency of bowel movements

• Diarrhea, constipation, or tenesmus after a bowel movement (a dull feeling as if stool remains)

• Bloody stool (bright red or dark red) or sticky mucus stool

• Stool that has become thinner than before

• Abdominal discomfort (abdominal pain, bloating)

• Loss of body weight or muscle strength

• Fatigue

• Loss of appetite, indigestion, nausea, and vomiting

• A mass, or lump-like object, felt in the abdomen

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• Symptoms of cancer vary depending on the location and type of the tumor. If a tumor develops in the cecum and ascending colon on the right side of the abdomen, it rarely causes intestinal obstruction because this area is wide and the stool is still loose. Instead, lesions in this area often cause chronic bleeding and the resulting anemia. On the other hand, lesions on the left side (descending colon and sigmoid colon) often cause symptoms of intestinal obstruction, and most patients complain of changes in bowel habits.

< Methods for Diagnosing Colorectal Cancer >

• Some colorectal cancers can be diagnosed with a digital rectal examination alone. After the age of 40, one digital rectal examination per year is recommended.

• Digital rectal examination: In this test, a doctor inserts a finger into the rectum while wearing a lubricated glove to check whether any abnormal lump can be felt.

• Carcinoembryonic antigen test: Carcinoembryonic antigen is a type of glycoprotein normally produced during fetal development. Production of this substance stops before normal birth. Therefore, if a higher CEA level than in newborns is found in an adult, it may indicate colorectal cancer or another cancer. However, CEA levels can also increase in liver diseases, including cirrhosis, in patients with alcoholic pancreatitis, and in smokers. Therefore, this test is used as an auxiliary method when determining the stage of cancer before surgery, checking the effectiveness of treatment, or confirming recurrence of cancer.

• Fecal occult blood test: Occult blood refers to blood mixed in urine or stool in such a small amount that it cannot be confirmed by chemical testing, or to such blood itself. The fecal occult blood test (simply, the occult blood test) is used to determine whether there is gastrointestinal bleeding or to detect colorectal cancer early. It can be performed at relatively low cost and without much discomfort, but its accuracy is limited, so both false negatives and false positives are common.

• Colonoscopy: Colonoscopy is a method of directly looking inside the colon by inserting a special camera, called an endoscope, through the anus. Endoscopes used today have a camera attached to the end of a flexible tube and connected by optical fiber. Because the doctor can directly observe the bleeding site and the surface of the lesion and assess the tissue condition, it is the most accurate diagnostic method for colon diseases. The advantage of colonoscopy is that it is highly sensitive for detecting colon polyps, and detected polyps can be removed immediately. The disadvantages are that bowel preparation is required before the test, the patient may feel discomfort if it is not performed under sedation, and if the colon lumen is blocked by cancer or another cause, the examination cannot proceed further.

• Double-contrast barium enema: In a double-contrast barium enema, a small tube is first inserted through the anus, and through it the contrast agent barium and air are introduced into the colon while the patient is asked to turn from side to side so that the barium spreads evenly over the colonic mucosa and the air expands the colon lumen. Images are then obtained with fluoroscopy. On the evening before the test, after eating a light meal such as rice porridge, the patient should take a prescribed laxative at night to remove all stool from the colon.

• Computed tomography: Computed tomography is a radiologic test useful not only for diagnosing colorectal cancer itself but also for evaluating the spread of the tumor. It is especially helpful when there is a possibility that the tumor has invaded surrounding tissues or other organs beyond the intestinal wall, and it is the most widely used method for checking whether there are metastases to the liver, lungs, lymph nodes, and elsewhere.

• CT virtual colonoscopy, also called CT colonography, is a diagnostic method that was introduced recently and has attracted attention. A small tube is inserted through the anus and only air or carbon dioxide is introduced to inflate the colon. Then thin-section continuous cross-sectional images are obtained using a spiral CT scanner, and computer software reconstructs them into three-dimensional multiplanar images, allowing the inside of the colon to be examined as if viewed with an endoscope. In other words, it is a technique for detecting colorectal cancer and colon polyps using three-dimensional virtual endoscopic images.

• Magnetic resonance imaging (MRI): For diagnosing colorectal cancer itself, MRI is not very suitable because it has several disadvantages compared with other tests, such as cost and the examination process. However, because the images are detailed enough to detect even small cancer cells of about 2 cm and are more accurate than CT for determining whether the tumor is malignant and whether it has metastasized to other organs, it is used as an additional or supplementary test when it is necessary to accurately identify the number of metastatic tumors in the liver.

• Abdominal ultrasound and rectal ultrasound: Abdominal ultrasound provides limited information for assessing abnormalities of the small and large intestines, so its sensitivity for diagnosing colorectal cancer is very low. Therefore, it is mainly used in combination with CT to assess metastasis to intra-abdominal organs rather than for diagnosing cancer itself. It is especially useful for detecting liver metastases.

• Positron emission tomography (PET) and PET/CT scans: Positron emission tomography is generally a test that takes advantage of the fact that cancer cells have faster metabolic activity than normal cells. After a glucose-based tracer labeled with a positron-emitting substance is injected, cancer cells are detected through the gamma rays emitted from this substance. However, the resulting images do not provide clear anatomical information, and sometimes lesions such as inflammation that are not cancer also appear positive. For this reason, PET/CT was developed, in which CT is performed together with PET and the results of the two tests are combined into a single image to overcome the shortcomings of PET alone.

Source: Korea Disease Control and Prevention Agency, National Health Information Portal