What Types of Cancer Can At-Home Tests Detect?
Worldwide, colorectal cancer is the fourth leading cause of cancer-related death, the third most common cancer among men, and the second most common cancer in women. Considering this predominance, it is no wonder that private and government entities, health experts and medical professionals are asking that all that people over the age of 45 screen for colorectal cancer. The preferred method for colorectal cancer is a colonoscopy, which can be not only expensive for many but also can feel invasive due to the nature of the bowel preparation and the procedure itself. Physicians who have patients that are at a low risk for colorectal cancer may be given the option to take an at home colon cancer test. Currently, there are three types of at home colon cancer tests that are typically prescribed by physicians to detect colorectal cancer.
Fecal immunochemical test (FIT). This test uses antibodies that specifically react with a blood protein in the stool. Physicians typically order the test to be repeated annually.
Guaiac-based fecal occult blood test (gFOBT). Conducted yearly, the gFOBT uses a chemical (guiac) to detect microscopic amounts of blood in the stool.
Stool DNA test (also known as FIT-DNA test). The most current stool test combines the FIT test with a test that can detect abnormally mutated DNA in the stool. Unlike the FIT and gFOBT, a stool DNA test can be repeated every three years if no abnormalities are found.
All three of these tests can accurately detect colorectal cancer through different methods, all of which will be explained in this article.
What Types of Cancers Can at Home Colon Cancer Tests Detect?
Polyps: Benign or Malignant?
At home colon cancer tests are used to detect colorectal neoplasms (abnormal growths or tumors) known as adenomas. The cells that make up these abnormal growths may be benign or malignant.
At home colon cancer tests are used to detect colorectal neoplasms (abnormal growths or tumors) known as adenomas. The cells that make up these abnormal growths may be benign or malignant. Benign colon neoplasms are called polyps and are found in several different forms. Some polyps may become malignant with time and develop into an adenocarcinoma, the most common form of colon cancer.
Polyp types and patterns of growth that may develop into colorectal cancer include:
Sessile serrated polyps (SSP). Serrated polyps have a saw tooth appearance under a microscope. A sessile polyp will appear flattened and broad at the base. There are three types of sessile polyps:
- Traditional serrated adenoma
- Sessile serrated polyp (SSP)
Studies have shown SSPs to be a precursor in 20-35% of colorectal cancer cases and are found in approximately 2-10% of patients undergoing screening for colon cancer.
Villous adenomatous polyps. An adenoma is a polyp that contains tissue that looks very similar to the normal lining of the colon. Colon cancer may originate in the cells of an adenoma. Adenomatous polyps are typically classified according to their shape and/or appearance, including:
- Villous -Round or oval polyp that resembles cauliflower
- Tubular – Small polyps that grow into a tube shape
- Tubulovillous – A combination of a villous and tubular growth pattern
Villous polyps may be associated with an increased risk of developing into colorectal cancer.
Number of polyps. Some people may develop several polyps in their colon. If a patient develops two or more polyps, their physician will typically place them in a higher risk category for colorectal cancer.
Size of polyp. Polyps larger than 1 centimeter in diameter have been shown to have an increased risk for becoming malignant.
Degree of dysplasia. A biopsy of a polyp will reveal the degree of dysplasia, or how much the polyp looks like cancer under a microscope. This is determined by a pathologist who will classify the cells as having a low-grade or high-grade dysplasia, or mild to severe rating respectively.
At Home Colon Cancer Tests, Large Adenomas, and Colorectal Cancer
At home colon cancer tests that detect blood in the stool are typically looking for the presence of a polyp, an abnormal tissue growth that may bleed when stool passes over its fragile surface. One test, Cologuard, also is able to detect the DNA of cancerous cells themselves. It is important to state that all three at home colorectal cancer screenings tests are accurate in detecting bleeding that stems from large adenomas and colorectal cancer. However, these tests must be followed up with a diagnostic colonoscopy which includes a biopsy of abnormal tissue to officially diagnose colon cancer.
At home colon cancer tests that detect blood in the stool are typically looking for the presence of a polyp, an abnormal tissue growth that may bleed when stool passes over its fragile surface. One test, Cologuard, also is able to detect the DNA of cancerous cells themselves.
Guaiac-based screening tests are a type of fecal occult blood test that can detect blood from a large adenoma or colorectal cancer. gFOBTs also are able to detect villous and tubulovillous polyps. The test works by using a chemical that changes color when it detects hemoglobin ( a blood protein). If you have received a positive result form a gFOBT, you most likely will be recommended by your physician to get a colonoscopy.
Like the gFOBT, the fecal immunochemical test (FIT) detects blood from larger, advanced adenomas and colorectal cancer. It reportedly has a higher sensitivity for detecting advanced adenomas than the gFOBT (42.6% vs. 23%). FIT screening is more sensitive than the gFOBT in all stages of colorectal cancer, from an adenoma to advanced neoplasia. Positive tests are usually followed up with a colonoscopy.
FIT-DNA tests are a combination of both FIT and DNA testing methods. It is also called stool DNA testing. Cologuard is able to detect genetic alteration in cells found in the stool that have sloughed off the lining of the intestines, including from polyps. This test is considered highly accurate (92.3%) in detecting blood and cancerous cells from stool samples. Stool DNA tests are considerable more sensitive to the detection of advanced neoplasms (42.4%) as compared to FIT alone (23.8%). A positive FIT-DNA test is usually followed up with a colonoscopy.
What Can At Home Colon Cancer Tests Not Diagnose?
Colonoscopies are ideal in the prevention and diagnosis of cancer because they allow the performing physician to visually inspect the colon and rectum to detect and remove polyps on site. A tissue sample, or biopsy, from the procedure can immediately be sent to a lab to be analyzed for cancerous cells. At home colon cancer tests are also effective in detecting certain types of polyps and colorectal cancers. However, there are some cases in which an at home test is not effective in the diagnosis of certain types of polyps that are known to have higher risk in developing colon cancer. Each at home test has a different level of accuracy for detecting these types. For instance, the FIT and FOBT have a poor sensitivity for detecting large adenomas and serrated polyps. Important notes to consider regarding what cancer at home colon cancer tests include:
- FIT and gFOBT have a low sensitivity for detecting both advanced adenomas and serrated polyps
- gFOBT and FIT are both less likely to detect small adenomas and sessile adenomas
- gFOBT has a high false-positive rate (from 15-30%) and requires dietary restrictions
- Cologuard has a 42.4% sensitivity for detecting advanced precancerous polyps
American Cancer Society. (2017, February 27). Understanding your pathology report: Colon polyps (sessile or traditional serrated adenomas. Retrieved from ACS: https://www.cancer.org/treatment/understanding-your-diagnosis/tests/understanding-your-pathology-report/colon-pathology/colon-polyps-sessile-or-traditional-serrated-adenomas.html
Burke, C.A. & Mankaney, G. (2017, March). Colorectal Neoplasia. Disease Management. Retrieved from Cleveland Clinic: https://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/gastroenterology/colorectal-neoplasia/
Chang, J.-J., et., al. (2020, November 10). Long term outcomes of colon polyps with high grade dysplasia following endoscopic resection. BMC Gastroenterology, 20, 376. Retrieved from PMC: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7656717/
Sovich, J. L., Sartor, Z., & Misra, S. (2015, October 04). Developments in screening tests and strategies for colorectal cancer. BioMed Research International, 326728. Retrieved from PMC: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4609363/
Tepus, M. & Yau, T. N. (2020, May 20). Non-invasive colorectal cancer screening: An overview. Gastrointestinal Tumors, 7, 62-73. Retrieved from PubMed: https://pubmed.ncbi.nlm.nih.gov/32903904/