Cancer Genetics and Epigenetics 2024, Vol.12, No.5, 254-269 http://medscipublisher.com/index.php/cge 255 2022). Moreover, the detection of CTCs can aid in monitoring disease progression and response to therapy, making it a versatile tool in cancer management (Marcuello et al., 2019; Yang et al., 2019; Green et al., 2021). This study evaluates the role of circulating tumor cells (CTCs) in the non-invasive diagnosis of colorectal cancer (CRC). Specifically, it summarizes the current state of research on the detection and characterization of CTCs in CRC patients, assesses the clinical utility of CTCs as biomarkers for early detection, prognosis, and monitoring of CRC, identifies the advantages and limitations of various CTC detection methods, and explores the potential of CTCs in guiding personalized treatment strategies and improving patient outcomes. By synthesizing the existing literature on CTCs in CRC, this study provides a comprehensive overview of their diagnostic potential and highlights directions for future research and clinical applications. 2 Overview of Colon Cancer 2.1 Pathogenesis and stages of colon cancer Colon cancer, also known as colorectal cancer (CRC), is a malignancy that originates in the colon or rectum (Fig.1.a). It is one of the most common cancers worldwide and a leading cause of cancer-related deaths. The development of colon cancer is a multistep process that involves genetic mutations and environmental factors. Early detection and diagnosis are crucial for improving patient outcomes and survival rates(Heidrich I et al. 2021 ). The pathogenesis of colon cancer involves a series of genetic and epigenetic changes that lead to the transformation of normal colonic epithelium into adenocarcinoma. This process typically follows the adenoma-carcinoma sequence, where benign adenomatous polyps gradually progress to malignant tumors. Key genetic mutations involved in this progression include alterations in the APC, KRAS, and TP53 genes, among others (Tie et al., 2019; Pan et al., 2021). Colon cancer is staged based on the extent of tumor invasion and spread, ranging from Stage I, where the cancer is confined to the inner lining of the colon, to Stage IV, where the cancer has metastasized to distant organs. The staging system helps guide treatment decisions and predict patient prognosis (Pan et al., 2021). Studies have shown that as cancer staging progresses, overall survival rates significantly decline, with Stage I patients having the highest survival rates, while Stage IV patients have the lowest. Additionally, over time, the risk for patients with advanced stages (Stages III and IV) increases significantly. 2.2 Current diagnostic methods and limitations Current diagnostic methods for colon cancer include a combination of clinical evaluation, imaging studies, and tissue biopsies. Colonoscopy is the gold standard for detecting and diagnosing colon cancer, allowing for direct visualization and biopsy of suspicious lesions. However, colonoscopy is invasive, requires bowel preparation, and carries risks such as perforation and bleeding (Cabel et al., 2017; Yang et al., 2019). Non-invasive diagnostic methods, such as fecal occult blood tests (FOBT) and fecal immunochemical tests (FIT), are also used for screening. These tests detect hidden blood in the stool, which can be an early sign of colon cancer. However, they have limitations in sensitivity and specificity, leading to false positives and negatives (Cabel et al., 2017; Yang et al., 2019). Imaging techniques, such as computed tomography (CT) colonography and magnetic resonance imaging (MRI), provide detailed images of the colon and surrounding structures. While these methods are less invasive than colonoscopy, they may still miss small or flat lesions and often require follow-up colonoscopy for confirmation (Cabel et al., 2017; Yang et al., 2019). The limitations of current diagnostic methods highlight the need for more accurate, non-invasive techniques. Circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) have emerged as promising biomarkers for the early detection and monitoring of colon cancer. CTCs are cancer cells that have shed from the primary tumor into the bloodstream, while ctDNA consists of fragmented DNA released by tumor cells. Both CTCs and ctDNA can be detected through liquid biopsy, a minimally invasive procedure that analyzes blood samples (Kantara et al., 2014; Shahjehan et al., 2019; Sundling and Lowe, 2019; Alese et al., 2022).
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