Digital rectal examination can be done in which a doctor examines the rectum for an abnormality by inserting a lubricated, gloved finger via the anus. This test can provide little information about cancer within the rectum or in nearby organs. Thus, detailed colorectal cancer investigations are required to establish the diagnosis of cancer. Some diagnostic techniques can accurately determine the extent of cancer invasion in the intestinal wall and spread of the disease to other body parts, which in turn help in selecting an appropriate treatment option. Following are some commonly used investigational tools for diagnosis of colorectal cancer:
1.Barium Enema/Double-Contrast Barium Enema (DCBE): In this test, a thick, viscous liquid containing barium (a heavy element that reflects x-rays) and the air is administered into the rectum and colon via the anus. Then, x-rays images are obtained for the lower abdomen where any polyps or cancer lesions are detected by the irregular barium coating. The test has relatively higher sensitivity for larger lesions and in symptomatic patients. It cannot be used to determine the extent of invasion or the spread of cancer to distant organs.
2. Colonoscopy: Colonoscopy is a diagnostic technique which uses a colonoscopy – a long, flexible, slender tube usually equipped with a camera, a light source, and some special instruments for biopsy or surgery. This enables the doctors to directly observe the lining of the rectum and entire colon to look for any abnormality. Biopsy samples are generally collected from abnormal areas.
3.Flexible sigmoidoscopy: This technique is very similar to with the only difference being the extent of the area examined during the test. Sigmoidoscopy helps in examining the distal part of the colon and the complete rectum.
4. Carcinoembryonic antigen (CEA): An elevated level of serum CEA may be associated with colorectal cancer, but it is of little value in detecting early-stage disease and may be false positive or false negative in some cases. This can, however, be useful in assessing the efficacy of the treatment/surgery and the progression/recurrence of the disease.
5. Laboratory Tests for Biopsy Samples: Biopsy samples contains a small piece of tissue, collected from the affected area with the help of a biopsy instrument. When subjected to various laboratory tests, these samples provide information about the type of cancer, the presence of specific defective genes or proteins, etc. The detected defects may then be targeted with a targeted therapy.
6. Imaging Tests: These tests are generally employed after the establishment of the pathological diagnosis. They help to diagnose the extent of locoregional invasion and spread of disease to the distant organs. Alternatively, these tests are employed after treatment to evaluate the treatment efficacy and to detect any signs of disease progression/recurrence.
-Computed tomography (CT) scan: In this technique, detailed cross-sectional images of body organs are generated using x-rays, with or without a contrast medium. It can help diagnose the spread of disease to nearby/distant lymph nodes and other organs, and may also be used to guide a biopsy needle into the affected area.
-Positron emission tomography (PET) scan: This technique uses a radioactive substance (fluorodeoxyglucose [FDG], etc) that is given via intravenous injection prior to the procedure. Cancer cells absorb larger amounts of the radioactive substance than normal cells. The areas of higher radioactivity indicate cancerous tissue on the PET scan. Thus, this technique can diagnose unsuspected spread of disease to distant body parts. It is usually combined with a CT scan (PET/CT).
-Magnetic resonance imaging (MRI) scan: This technique provides detailed images of tissues inside the body using radio waves, a strong magnetic field, and gadolinium contrast. It can accurately diagnose the extent of invasion and spread of disease to nearby/distant body parts.
Guaiac-based fecal occult blood test (gFOBT), immunochemical fecal occult blood test (iFOBT), and stool DNA test are some other useful screening techniques which might help in the diagnosis of occult disease.
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