Dr Angela Nunnery and Dr Millard D Collins are family medicine doctors who know about the importance of colorectal cancer screening. They are passionate about prevention and advocate for early detection of cancerous tissue. Both recommend regular screening for colorectal cancer in order to make sure that any colon polyp will be detected and removed ideally before it can develop into cancer.

They are co-authors of the soon-to-be-published “Colorectal Cancer Screening Modalities”, a resource for health care professionals. It illustrates the current recommendations on screening for colorectal cancer and gives a profound overview of the screening modalities that are available as well as in development in the USA. For this interview for Colorectal Cancer Awareness Month, which is held in March, we wanted to know more about the different screening methods from the patients’ perspective.


Dr. Nunnery, Dr. Collins, there are basically three types of tests to detect and diagnose colorectal cancer: visualization tests, stool-based tests, and blood assay tests. What are the pros and cons of each type of test?

 There are three types of tests, as stated:

  • Visualization tests include colonoscopy, flexible sigmoidoscopy, and CT (computed tomography) colonoscopy. Visualization tests can show the various landmarks of the colonic areas explored and provide information as to the size, shape, and composition of masses seen. Colonoscopy and flexible sigmoidoscopy can both also take biopsies of lesions seen, and often better characterize the lesion prior to biopsy results. These modalities also eliminate the need for follow-up testing that occurs with other modalities if there are findings on screening. Those other modalities require colonoscopy if screenings are positive. This includes CT colonoscopy, which can visualize, but cannot attain biopsy samples. Cons associated with visualization testing include the need for bowel preparation, variations based on the skill of the specialist performing the exam, and risk of perforation.
  • Stool-based tests include gFOBT (guaiac-based fecal occult blood test) and FIT (fecal immunochemical test). These tests are done to screen blood present in samples of stools to be provided. Advantages of these tests include being cheaper, widely available, and non-invasive. Disadvantages include the handling of stool (to create the sample and to process it), inability to differentiate non-colonic causes of bleeding or altered samples based on medications or food, and the requirement for visualization follow-up on positive screenings (i.e. colonoscopy).
  • Blood assay tests are new and promising technologies that are emerging, such as MT-sDNA (multitarget stool DNA). The pros would include its reported abilities to capture evidence of lesions of all types, including precancerous polyps to cancerous lesions at various stages. Also, this testing would be non-invasive. Cons would include expense at this point, high false positives, and the need for visualization follow-up on positive screenings (i.e. colonoscopy)


How do healthcare professionals decide which method to use for each individual patient?

Healthcare providers consider several factors when deciding which method to use for each individual: costs, convenience, and the patient’s medical history and possible medication interactions. Ultimately, all viable options should be discussed with the patient while discussing the pros and cons of each. Patient preference is the option most commonly chosen.

There may be some in-depth discussion when considering the risks factors present, previous tests and associated findings, and the potential for follow-up. In select cases, the option for colonoscopy may be selected when the likelihood of biopsy is extremely high due to reasons stated above.


Invasive screening methods are considered more effective than non-invasive screening methods. Why are non-invasive methods still being used?

Non-invasive methods are still being used for several reasons when it comes to screening for colorectal cancer. Cheaper costs associated with these test options are big ones. It is critical to eliminate the need for anesthesia and a facility charge associated with invasive screening options. The convenience of being able to do the test in the comfort of one’s own home makes it attractive for many. Some patients have considerations that may make anesthesia or mobility a challenge, including medical conditions, medications, and other things (morbid obesity, quadriplegia, stroke deficits, anatomic colonic variants). Furthermore, non-invasive methods are still highly effective for detecting colorectal cancer at various stages, thus impacting mortality rates. Their main drawback is the need for colonoscopy in the event of a positive screening.


What are the key barriers identified that can prevent a person from going for a colorectal cancer screening? How can these barriers be overcome?

Some of the key barriers preventing a person from going for colorectal screening include costs, fear of the procedure or results, past experiences that were unsatisfactory in the healthcare setting, not being made aware of the recommended testing method or interval by their provider, not having a routine provider, and lack of insight due to a medical condition (i.e. mental issue or substance abuse).

These barriers can be overcome through constant engaging of both patients as well as providers on the up-to-date guidelines, recommendations and characteristics of each, and removal of any stigma associated with receiving these services. There should also be funding available for screening of cancers that can be detected early to improve access and decrease morbidity and mortality associated with development of colorectal cancer.


New methods of screening are being developed and tested, such as detecting circulating tumor cells in the blood stream. What makes you think that these new methods will eventually become the norm for colorectal cancer screening and methods like colonoscopies will be a thing of the past?

While there is agreement that new blood testing modalities show promise in the early detection of colorectal cancers in selected patients, the data is too preliminary to reach this conclusion. Similarly, while they can pick up evidence of the presence of tumors, the premise is that cells have been released into the blood stream and no information is provided as to where in the colon such lesions are located. As such, colonoscopies would still be needed to follow up any positive screens. This visualization technique is likely here to stay.


Many thanks for your time and for the interview.

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