Regular screening and removal of precancerous polyps are crucial to preventing rectal cancer. Screening increases the likelihood of finding and treating cancer in its earliest stage, when the cure rate is high. Mayo Clinic uses the screening and diagnostic tests below. In tests that involve radiation, specialists carefully monitor doses to avoid the risk of radiation overexposure.
- Colonoscopy. Colonoscopy is generally considered the best screening and diagnostic test for rectal cancer. If your doctor discovers small polyps during the exam, they are usually removed immediately. Large polyps and tumors require surgical removal. In such cases, the doctor can mark them during colonoscopy to help guide future surgery.
- Sigmoidoscopy. For this exam, doctors use a flexible, fiber-optic tube to examine your rectum and sigmoid colon — the last two feet (61 centimeters) of the large intestine. A sigmoidoscopy can detect rectal polyps and cancer, but it can't identify problems higher in your colon.
- Virtual colonoscopy. A minimally invasive alternative to traditional colonoscopy, virtual colonoscopy uses a CT scanner to detect polyps, but polyps can't be removed during this test. If polyps are found during the procedure, your doctor can perform a traditional colonoscopy to remove them the same day or next day.
- Probe-based laser confocal endomicroscopy. The confocal laser endomicroscopy probe system enables experts to analyze colon polyps during colonoscopy instead of in the lab. A miniature microscope probe can provide the same level of detail that a pathologist sees during analysis under a lab microscope. This means that your doctor can target removal of only cancerous or precancerous polyps, sparing you unnecessary procedures.
- DNA stool tests. Colon polyps and cancers continuously shed mutated cells that eventually make their way into stool. Analyzing these cells for genetic mutations may detect polyps and early-stage cancers. Although not yet widely used, this test is likely to become more common in the future.
- Staging tests. Identifying the extent and spread of the disease is essential for choosing the best treatment for you. Staging tests, such as computerized tomography (CT), positron emission tomography (PET) scan and X-rays help your doctor determine how deeply the cancer has invaded the colon wall and whether it spread to nearby lymph nodes or organs. Your doctor may perform a colonoscopy and endoscopic ultrasound of the rectum, mark the location of a lesion, and then perform an ultrasound-guided fine-needle aspiration of any suspicious lymph nodes.
Read about colonoscopy, virtual colonoscopy, endoscopy, ultrasound, PET scan and CT scan.