Dra. Rosa Neto da Silva

Gastroenterologist

Dra. Isabel Jardim

Gastroenterologist

Screening for colorectal cancer
Its importance and effectiveness

HPA Magazine 20

When we talk about screening for digestive diseases, it immediately brings us to the colorectal cancer (CRC), in the form of adenocarcinoma in 98% of cases. These tumors are more common in developed countries, being the second most common type of cancer in Europe, affecting over half a million people annually. Given its importance, the European Commission Initiative on Colorectal Cancer (ECCIC) was created to establish guidelines for screening and treatment of CRC to be implemented in European countries, based on the updated scientific evidence.

In Portugal, around 10,000 new cases are diagnosed each year, and on average, 11 people die daily from this disease, making it the leading cause of cancer-related deaths. With timely diagnosis, the survival rate for patients with early-stage CRC exceeds 90%. However, despite the screening, which is the primary means of early detection of these tumors, is still not a national reality due to disparities in response to established programs and lack of access and/or adherence by the population.
Colorectal cancer affects both sexes and its incidence increases from the age of 35, with 85% to 90% of cases diagnosed in individuals above 50 years of age across all social strata. It is multifactorial, with identified factors including genetic predisposition and lifestyle factors, such as smoking, excessive alcohol consumption, a diet high in saturated fats, dyslipidemia, obesity, sedentary lifestyle, and exposure to certain industrial chemicals. Hence, the importance of Digestive Health.
The existence of a personal and/or family history of polyps at risk or of colorectal cancer, especially in first-degree relatives, is also associated with an increased risk, the lower the age at diagnosis, the higher the risk. Individuals belonging to families with hereditary cancer syndromes (classified as high risk) are included in specific screening and surveillance programs.
These hereditary cancer syndromes are the result of genetic mutations (pathogenic variants) in our DNA that may be transmitted to offspring, significantly increasing the risk of oncological disease in individuals from these families. Currently, it is estimated that these syndromes account for about 10-15% of cancer cases. In these families, we often find individuals who are young at the time of cancer diagnosis, individuals who have had more than one tumor (malignant, benign, or both) regardless of age, tumors with certain histological characteristics, multiple generations of the same affected family, or the presence of rare tumors. The forms of hereditary CRC syndrome are divided into non-polyposis hereditary colorectal cancer (e.g., Lynch Syndrome) and colonic polyposis-associated (e.g., Familial Adenomatous Polyposis associated with the APC gene or the MUTYH gene).
 

The screening aims to diagnose (ideally) precancerous lesions of CRC, such as adenomas/sessile serrated lesions, or early-stage CRC in asymptomatic individuals between the ages of 50 and 75 without other associated risk factors (average risk). After the age of 76 and up to 85, the decision to undergo screening should be individualized based on the person's health status. Above the age of 85 or when the estimated survival is less than 10 years, it is not recommended.
If there is a first-degree relative with CRC (or high-risk adenoma), the age of screening initiation should be reduced to 40 years or 10 years before on the youngest affected member in the family.
An approach to the currently available screening tests is to divide them into direct tests (colonoscopy) and indirect tests (all other available tests, including computed tomography colonography (CT or virtual colonoscopy), flexible sigmoidoscopy, different fecal tests, and colon capsule endoscopy). These last two tests have limitations in diagnosing sessile serrated lesions (flat lesions) and require a colonoscopy when positive to complete the screening process.
Colonoscopy remains the gold standard for screening as it is the only direct test that allows for both diagnosis and therapeutic intervention of precursor lesions, as well as sample collection and marking of lesions for subsequent surgical approach in suspected CRC cases. However, it has limitations such as requiring prior diet and preparation, being an invasive procedure, and having significant economic costs. Additionally, there is an insufficient number of digestive endoscopy units, as well as medical and nursing specialists currently available for mass screening.
In its latest review, the American College of Gastroenterology recommended colonoscopy or fecal immunochemical testing (FIT) as the first choices for CRC screening, with colonoscopy reserved for individuals with affected first-degree relatives. The remaining tests were suggested for individuals who are unable or refuse to undergo the first-line tests. 
The recommended intervals for the different tests, when negative, are 1 year for FIT, 10 years for colonoscopy, 3 years for fecal DNA testing, and 5 years for flexible sigmoidoscopy, computed tomography colonography, and colon capsule endoscopy.
It was also recommended to implement organized screening programs for at least 80% of the eligible population, ensuring better adherence through the use of methods that guarantee higher participation rates. Equally important is the registration and evaluation of results, with prompt follow-up for positive cases to ensure timely colonoscopy. Only by ensuring these premises will be possible to reduce the incidence and mortality of colorectal cancer in the future.