CRC Screening: Guiding our patients through the options

CRC SCREENING:

GUIDING OUR PATIENTS THROUGH THE OPTIONS

By Ashithkumar Beloor-Suresh Ana Maria Lopez

Colorectal cancer (CRC) is a common cancer that can be detected early in the carcinogenesis process making it an ideal target for cancer screening. Thought to be due to multiple carcinogenic “hits,” CRC precursors in the form of polyps may be identified prior to frank malignancy. Approaches to CRC screening include direct visual techniques and stool-based techniques. The former has the advantage of being diagno-peutic or both diagnostic and therapeutic. The lesion or polyp may be identified through direct visualization and removed for diagnostic evaluation. This action also serves to arrest the carcinogenic process at that anatomical location. Direct visualization requires an appropriate bowel prep with full evacuation. For people who may have difficulty with this process, stool-based studies may be more acceptable. This article is intended to be of help as background for our conversations with our patients about CRC screening. These conversations can help guide patients through the data and help them make sense of the options and identify the study that will be most acceptable to them.

Epidemiology:

CRC is the third most common cancer worldwide, excluding non-melanoma skin cancer. CRC appears to peak in incidence between 65-74 years of age; however, the incidence of CRC in adults aged 40 to 49 years has increased by almost 15% from 2000-2002 to 2014-2016. [1] It is estimated that 10.5% of new CRC diagnoses occur in persons younger than 50 years. [2] The incidence of CRC is also reported to be higher in Black/African, American Indian, and Alaskan Native adults, persons with a family history of CRC or inherited genetic syndromes such as Lynch syndrome or familial adenomatous polyposis, men, and persons with other risk factors such as obesity, diabetes, long-term smoking, and unhealthy alcohol use. The reason for higher incidence may be related to multiple factors including access to care, underlying co-morbidities, and molecular or genetic factors. These factors remain under active investigation. [3] CRC screening that identifies pre-malignant or early malignant lesions can play a vital role in decreasing both CRC incidence and mortality.

Updated US Preventive Services Task Force (USPSTF) Recommendations on CRC Screening:

The USPSTF updated its CRC screening guidelines earlier this year to recommend CRC screening in people aged 50-75 years with substantial net benefit and those between 45-49 years of age with moderate net benefit. In people aged 76-85 years, CRC screening has a small net benefit, and people who have never been screened for CRC in this age group are more likely to benefit.

This recommendation applies to asymptomatic adults 45 years or older who are at average risk of CRC (no prior diagnosis of CRC, adenomatous polyps, or inflammatory bowel disease; no personal diagnosis or family history of known genetic disorders that predispose them to a high lifetime risk of CRC—such as Lynch syndrome or familial adenomatous polyposis). Those with a history of these conditions would not be at average risk for CRC and would be considered for high-risk care.

CRC Screening Tests:

The various recommended tests are based either on stool-based examinations or visualization of the gut through endoscopic or imaging techniques. The options differ based on their effectiveness, convenience, cost, availability, safety, and patient acceptance. The recommendations for screening for

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CRC discussed in this review do not include serum tests, urine tests, stool-based tests requiring multiple tests, or capsule endoscopy for CRC due to limited evidence and/or lack of efficacy in comparison to the studies presented.

According to the USPSTF, there is no particular best test. The best test is the one the patient is most likely to complete.

1) Stool-Based Tests:

Stool-based tests include the Fecal Immunochemical Test (FIT) and the Multitarget stool DNA tests with fecal immunochemical testing (sDNA- FIT).

Fecal Immunochemical Test (FIT): tests for the presence of hemoglobin in the stool sample using antibodies. This increases the accuracy of detection over the traditional guaiac fecal occult blood test. The patient collects and returns the stool sample in a specially designed FIT kit within 24 hours from collection to prevent false negatives due to hemoglobin degradation. FIT is recommended annually starting at 45 years of age.

Multitarget stool DNA tests with fecal immunochemical

testing (sDNA-FIT): It tests for specific DNA biomarkers present in the cells shed from the colon and rectum along with the FIT component, and only the combination of these two tests is currently approved by the FDA. The patient returns the specially designed kit to the lab with a single stool sample within 72 hours. It is recommended every 1- 3 years.

All positive stool-based testing require colonoscopy for further management. [4] Stool-based tests have the advantage of being done at home, at the time of the patient’s choosing, and in a non-invasive manner. They do not require bowel preparation, unlike direct visualization tests. With more frequent screening intervals, a long-term commitment to screening activity helps achieve its benefit.

2) Visualization:

Visualization may take place directly through endoscopy or indirectly through imaging.

Endoscopy: The primary approach for direct visualization of the colon for cancer screening is colonoscopy. Although flexible sigmoidoscopy allows for direct visualization, its view of the colon is limited and incomplete. Direct visualization approaches allow for diagnostic biopsies which may result in therapeutic interventions if the lesion can be fully excised at the time of diagnosis. If normal, subsequent colonoscopy in average risk individuals is recommended every ten years.

Imaging: Computed Tomography (CT) Colonography, or virtual colonoscopy, utilizes CT imaging techniques to construct 2D/3D images of the colon to facilitate visualization of abnormalities on the surface of the colon. These changes may correspond to premalignant or malignant changes and would need follow-up with direct visualization, colonoscopy. Unlike colonoscopy, if normal, subsequent virtual colonoscopy in average risk individuals is recommended every five years.

These visualization studies provide the advantage of longer intervals between screenings; however, the studies cannot be performed at home and require bowel preparation and the expertise of a medical professional. These studies also carry the risk of complications from sedation and instrumentation like bleeding or perforation.

When to stop CRC screening:

The current recommendations are to continue screening in average-risk individuals until 75 years of age. Considerations of life-limiting co-morbidities are always necessary. As our population ages healthfully, there will be more persons 76-85 years of age whose individualized risk for cancer, life expectancy, and comorbidities will demonstrate a benefit for screening. Generally, screening in persons over 85, is not recommended.