Circulating Tumor Cells in Gastrointestinal Cancers: Current Status and Future Perspectives

CTCs are tumor cells present in the blood circulation that play a critical role in cancer progression, especially for tumor metastasis and recurrence. Academics have been studying CTCs for decades, and a variety of sensitive and specific techniques are now available to achieve the isolation and identification of CTCs. On this basis, clinicians have also gradually gained a deeper understanding of the significance of CTC in the clinical diagnosis and treatment of various tumors through various clinical studies.

CTC testing is an important type of "liquid biopsy" that provides important information for predicting patient survival, monitoring response/drug resistance, evaluating microscopic residual disease (MRD), assessing distant metastasis, and evaluating treatment options. Currently, there are clinical studies which suggest that elimination of CTC in the blood is one of the effective means of preventing tumor metastasis and even treating tumors. However, the clinical application of CTC is still facing clinical and technical challenges, and the summary of CTC detection technology and clinical significance applied in tumor diagnosis and treatment, especially in gastrointestinal tumors, will help us to further clarify how to effectively utilize CTC detection to serve the patients at this stage, as well as to clarify the direction of CTC in gastrointestinal tumor diagnosis and treatment research.

The ideal CTC separation technique needs to have the following characteristics.

(1) the ability to isolate all types of CTCs;

(2) The ability to effectively exclude interference caused by normal blood cells;

(3) Accurately identify suspected CTCs.

In current CTC assay technology, which is generally divided into two steps, enrichment and identification,

There are mainly these types:

1.CTC technology based on immunoaffinity, including positive enrichment and negative enrichment, as well as microfluidic technology for cellular functionalization;

2.CTC techniques based on biological properties, including density gradient centrifugation, cell filtration, inertial properties and bioelectric fields.

Immunoaffinity-based CTC technology, represented by the FDA-approved Cellsearch, although widely used in gastric and colorectal cancers in recent years, has resulted in very little CTC capture due to the fact that it focuses only on the capture of CTCs of a certain immunophenotype, ignoring the impact of EMT transformation in the formation and metastasis of CTCs, and ignoring the role of some specific CTC subpopulations.

The most common biophysical methods for CTC enrichment are cell-size-based isolation. These techniques provide in situ platforms for fluorescence in situ hybridization (FISH), immunofluorescence (IF), genomic and transcriptomic sequencing, and this technology also provides opportunities for in vitro culture of CTCs, which lays an important foundation for further understanding of the biology of CTCs. The paper highlights the CTCBIOPSY technology of YZY?Med, its clinical application and the progress of obtaining the registration license in China.

The clinical significance of CTC in gastrointestinal tumors is mainly reflected in the aspects of prognosis assessment, metastasis monitoring, efficacy evaluation and early diagnosis.

The role of CTC in patient prognostic stratification in GC (gastric cancer) and CRC (colorectal cancer) are the most studied aspects of CTC clinically and have been confirmed by numerous studies. For GC and CRC, CTC is considered to be significantly associated with disease progression and patient prognosis. Previously, a team from the Department of Gastrointestinal Surgery at Central South Hospital recruited 138 patients with stage I-III colorectal cancer for a prospective cohort study to evaluate the prognostic value of changes in CTC counts before and after radical surgery, and found that postoperative CTC positivity but preoperative CTC negativity was an independent indicator of a poor prognosis, and that patients with preoperative CTC positivity that converted to negativity after surgery had a prognosis consistent with that of patients with preoperative CTC negativity. Meanwhile, other studies have shown that CTC detection at different time points during treatment may have different prognostic significance, which may be due to the evolution with time and treatment, in which the screening pressure of surgery, chemotherapy, and radiotherapy and this tumor-killing immunity can stimulate the expansion of tumor subclones, resulting in changes in the number and molecular characteristics of CTCs. Rigorous selection of time points for CTC testing and repeat CTC testing is necessary to overcome genetic changes in CTCs due to anticancer therapies and thus accurately assess patient prognosis.

In efficacy evaluation, studies have shown that baseline CTC testing can be used to evaluate response to systemic therapy in GI tumors. Several studies have also confirmed the predictive value of CTC testing in chemotherapy, for example, changes in CTC after treatment can help to quickly identify ineffective treatment in patients with advanced gastric cancer, and the CRC study also found a significantly higher rate of disease progression in patients with positive CTC after 3-4 weeks of chemotherapy.

In the early diagnosis of disease, tumor cells may separate from the primary tumor and enter the bloodstream, providing a theoretical basis for the use of CTCs testing as an early diagnostic tool. In the past few years, several studies have explored the early diagnostic value of CTCs, based on different methods of CTC testing for gastrointestinal malignancies, and the percentage of positive patients was found to be considered too low to obtain a sensitivity that is sufficiently true for early diagnosis. Therefore, screening the general population with CTC assessment is logistically unrealistic, but may be realistic in practical applications in high-risk populations, such as those with a family history of gastrointestinal tumors.

In order to achieve clinical use of CTC for gastrointestinal tumors, clinicians first need a universally accepted, rapid, low-cost technique for CTC detection and identification with accurate results. Also, standardized procedures for detection must be established. Then, clinical studies of CTC as a circulating marker need to be conducted and validated in large-scale, long-term follow-up, prospective clinical trials to ensure its clinical applicability. In addition, additional basic research to gain insight into cancer biology can provide new insights into how and when CTC testing can be performed for optimal clinical application. Despite these obstacles, there is good reason to believe that with advances in detection, identification, and downstream analysis technologies, CTC will provide a wealth of valuable information for the clinical diagnosis and treatment of patients with gastrointestinal tumors in the near future.

Four years after the publication of this review, in November 2023, the Gastric Cancer Group of the Oncology Branch of the Chinese Medical Association, the Colorectal Tumor Committee of the Chinese Medical Doctors' Association, the Colorectal Cancer Committee of the Chinese Anti-cancer Association, the Gastric Cancer Committee of the Chinese Anti-Cancer Association, and the Gastrointestinal Tract Polyps and Pre-cancerous Lesions Committee of the Chinese Anti-cancer Association, the expert consensus of the "Chinese Expert Consensus on the Application of Circulating Tumor Cell Testing in the Diagnosis and Treatment of Gastrointestinal Tract Tumors (2023 Edition)", which was jointly initiated by the Chinese Medical Association, Chinese Medical Doctors' Association and Chinese Anti-Cancer Association), and after years of careful preparation by Zhiyou medical and clinical experts, the expert consensus "Chinese Expert Consensus on the Application of Circulating Tumor Cells Detection in the Diagnosis and Treatment of Gastrointestinal Tumors (2023 Edition)" was published simultaneously in the Chinese Journal of Gastrointestinal Surgery and Journal of Practical Oncology, which revolves around the detection technology and clinical application of CTC detection in the diagnosis and treatment of GI tumors, including prognostic judgment, recurrence, and prognostication, as well as the use of CTC in the treatment of GI tumors. It discusses and formulates 7 consensus recommendations on the application of CTC testing in the diagnosis and treatment of gastrointestinal tumors, including prognostic judgment, monitoring of recurrence and metastasis, efficacy monitoring and auxiliary diagnosis, which provides reference standards for clinical application.

Reference：

[1]Yang C, Chen F, Wang S, Xiong B. Circulating Tumor Cells in Gastrointestinal Cancers: Current Status and Future Perspectives. Front Oncol. 2019 Dec 13;9:1427.

[2]Gastric Cancer Group, Oncology Branch, Chinese Medical Association; Colorectal Cancer Professional Committee, Chinese Medical Doctor Association; Colorectal Cancer Professional Committee, Chinese Anti-Cancer Association; Gastric Cancer Professional Committee, Chinese Anti-Cancer Association; Digestive Tract Polyp and Precancerous Lesion Professional Committee, Chinese Anti-Cancer Association.

[3]Chinese expert consensus on the application of circulating tumor cell detection in the diagnosis and treatment of gastrointestinal neoplasms (2023 edition)]. Zhonghua Wei Chang Wai Ke Za Zhi. 2023 Nov 25;26(11):1001-1007.