New Diagnostics Methods for Colorectal Cancer Early-Detection

Abstract

Colorectal Cancer (CRC) is currently one of the main public health challenges in Western countries. In many countries, it is the most prevalent cancer, and it is estimated that 2 million new cases have arisen worldwide in 2020 [1]. CRC has a relatively low 5-year survival rate of 50%, even though, if it is diagnosed in its earliest stages, survival increases to 95% [2]. The problem is that survival is only 8% if the diagnosis is made in the late stages of cancer. Given these data, we should ask why such a high number of CRC are diagnosed in their later stages. In most advanced countries, the population has access to annual or biannual screening campaigns. This screening system is based on Faecal Immunochemical Test (FIT) in many countries and tries to identify traces of blood in the stool. If a patient has a positive FIT test, a colonoscopy is recommended because the chances of having polyps (the precancerous lesion) or CRC is increased. Colonoscopy is the standard diagnostic method for two reasons. The first is that is the only imaging technique able to remove polyps in the same endoscopic intervention, causing less discomfort to the patient. The second is that, if a cancer is diagnosed, biopsies are obtained to confirm it and a surgical operation is prescribed to ensure the complete removal of the malignant cells. However, colonoscopy is not perfect and may miss some lesions and requires preparation that is very uncomfortable for patients. In recent times, a significant number of technologies have appeared for the early detection of CRC, the liquid biopsy standing out among all of them. Liquid biopsy allows, through a simple blood draw, to know if a patient has CRC, even in its most preliminary stages [3]. However, the liquid biopsy does not replace colonoscopy since, if CRC is suspected, what is recommended in clinical practice is to proceed with a colonoscopic examination.But why is colonoscopy not a 100% reliable method? Experts estimate that, on average, 22% of polyps are missed at colonoscopy [4]. The reasons are multiple, for example, the colonoscope camera has a very limited range of vision −180°−, some polyps can "hide" behind the multiple folds of the colon or be "overshadowed" by remains of faeces if the patient is not well prepared or even if the endoscopist does not identify them [5]. In fact, there are several studies that correlate the endoscopist's hours of experience with their Adenoma Detection Rate (ADR) that is the most important parameter related with CRC prevention [6]. Other studies have reported how this ADR can vary for the same endoscopist as the day progresses and he accumulates more fatigue. Because of all these factors, today, 8% of colorectal CRC are interval cancers, that is, cancers that are diagnosed after a negative colonoscopy [7]. To