Clinical significance of circulating plasma DNA in gastric cancer

Recent advances in gastric cancer early diagnosis

Gastric cancer (GC) remains an important cause of cancer death worldwide with a high mortality rate due to the fact that the majority of GC cases are diagnosed at an advanced stage when the prognosis is poor and the treatment options are limited. Unfortunately, the existing circulating biomarkers for GC diagnosis and prognosis display low sensitivity and specificity and the GC diagnosis is based only on the invasive procedures such as upper digestive endoscopy. There is a huge need for less invasive or non-invasive tests but also highly specific biomarkers in case of GC. Body fluids such as peripheral blood, urine or saliva, stomach wash/gastric juice could be a source of specific biomarkers, providing important data for screening and diagnosis in GC. This review summarized the recently discovered circulating molecules such as microRNAs, long non-coding RNAs, circular RNAs, which hold the promise to develop new strategies for early diagnosis of GC.

Limited Sensitivity of Circulating Tumor DNA Detection by Droplet Digital PCR in Non-Metastatic Operable Gastric Cancer Patients

This study was designed to monitor circulating tumor DNA (ctDNA) levels during perioperative chemotherapy in patients with non-metastatic gastric adenocarcinoma. Plasma samples were prospectively collected in patients undergoing perioperative chemotherapy for non-metastatic gastric adenocarcinoma (excluding T1N0) prior to the initiation of perioperative chemotherapy, before and after surgery (NCT02220556). In each patient, mutations retrieved by targeted next-generation sequencing (NGS) on tumor samples were then tracked in circulating cell-free DNA from 4 mL of plasma by droplet digital PCR. Thirty-two patients with a diagnosis of non-metastatic gastric adenocarcinoma were included. A trackable mutation was identified in the tumor in 20 patients, seven of whom experienced relapse during follow-up. ctDNA was detectable in four patients (N = 4/19, sensitivity: 21%; 95% confidence interval CI = 8.5–43%, no baseline plasma sample was available for one patient), with a median allelic frequency (MAF) of 1.6% (range: 0.8–2.3%). No patient with available plasma samples (N = 0/18) had detectable ctDNA levels before surgery. After surgery, one of the 13 patients with available plasma samples had a detectable ctDNA level with a low allelic frequency (0.7%); this patient experienced a very short-term distant relapse only 3 months after surgery. No ctDNA was detected after surgery in the other four patients with available plasma samples who experienced a later relapse (median = 14.4, range: 9.3–26 months). ctDNA monitoring during preoperative chemotherapy and after surgery does not appear to be a useful tool in clinical practice for non-metastatic gastric cancer to predict the efficacy of chemotherapy and subsequent relapse, essentially due to the poor sensitivity of ctDNA detection.

Identification of DNA mutations in gastric washes from gastric adenocarcinoma patients: Possible implications for liquid biopsies and patient follow-up

Whereas cancer patients have benefited from liquid biopsies, the scenario for gastric adenocarcinoma (GAC) is still dismal. We used next-generation deep sequencing of TP53-a highly mutated and informative gene in GAC-to assess mutations in tumor biopsies, plasma (PL) and stomach fluids (gastric wash-GW). We evaluated their potential to reveal tumor-derived mutations, useful for monitoring mutational dynamics at diagnosis, progression and treatment. Exon-capture libraries were constructed from 46 patients including tumor biopsies, GW and PL pre and post-treatment (196 samples), with high vertical coverage >8,000×. At diagnosis, we detected TP53 mutations in 15/46 biopsies (32.6%), 7/46 GW- (15.2%) and 6/46 PL-samples (13%). Biopsies and GW were concordant in 38/46 cases (82.6%) for the presence/absence of mutations and, furthermore, four GW-exclusive mutations were identified, suggesting tumor heterogeneity. Considering the combined analysis of GW and PL, TP53 mutations found in biopsies were also identified in 9/15 (60%) of cases, the highest detection level reported for GAC. Our study indicates that GW could be useful to track DNA alterations, especially if anchored to a comprehensive gene-panel designed for this malignancy.

Comparison of the Clinicopathological Characteristics and Genetic Alterations Between Patients with Gastric Cancer with or Without Helicobacter pylori Infection

BACKGROUND

Helicobacter pylori (HP) can induce epithelial cells and intestinal metaplasia with genetic damage that makes them highly susceptible to the development of gastric cancer (GC).

MATERIALS AND METHODS

Between 2005 and 2010, 356 patients with gastric cancer who received curative surgery were enrolled. Analysis of HP, Epstein-Barr virus (EBV) infection, PIK3CA amplification, and mutation analysis of 68 mutations in eight genes using a mass spectrometric single-nucleotide polymorphism genotyping technology was conducted. The clinicopathological characteristics of patients with or without HP infection were compared.

RESULTS

Among the 356 patients, 185 (52.0%) had HP infection. For intestinal-type GC, patients with HP infection were more likely to be younger and had fewer PI3K/AKT pathway genetic mutations than those without HP infection. For diffuse-type GC, patients with HP infection were characterized by less male predominance, less lymphoid stroma, fewer microsatellite instability-high tumors, and fewer PI3K/AKT pathway genetic mutations than those without HP infection. Patients with HP infection had less tumor recurrence and a better 5-year overall survival (87.7% vs. 73.9%, p = .012) and disease-free survival (64.1% vs. 51.3%, p = .013) than those without HP infection, especially for intestinal-type GC. For EBV-negative GC, patients with HP infection had fewer PI3K/AKT pathway mutations and a better 5-year overall survival and disease-free survival than those without HP infection. Multivariate analysis demonstrated that HP infection was an independent prognostic factor regarding overall survival and disease-free survival.

CONCLUSION

Patients with GC with HP infection were associated with fewer PI3K/AKT pathway genetic mutations and better survival than those without HP infection, especially for EBV-negative and intestinal-type GC.

IMPLICATIONS FOR PRACTICE

Patients with gastric cancer with Helicobacter pylori (HP) infection had fewer PI3K/AKT pathway genetic mutations, less tumor recurrence, and better survival than those without HP infection, especially for Epstein-Barr virus (EBV)-negative and intestinal-type gastric cancer. HP infection is an independent prognostic factor regarding overall survival and disease-free survival. Future in vivo and in vitro studies of the correlation among HP infection, PI3K/AKT pathway, and EBV infection in gastric cancer are required.

Tumor-specific genetic aberrations in cell-free DNA of gastroesophageal cancer patients

The applicability of liquid biopsies is studied intensively in all types of cancer and analysis of circulating tumor DNA (ctDNA) has recently been implemented clinically for mutation detection in lung cancer. ctDNA may provide information about tumor quantity and mutations present in the tumor, and as such have many potential applications in diagnosis and treatment of cancer. It has been suggested that ctDNA analysis may overcome the issue of intra-tumor heterogeneity faced by tissue biopsies and serve as an additional diagnostic tool. Furthermore, liquid biopsies are potentially helpful for monitoring of treatment response as well as detection of minimal residual disease and relapse. Gastroesophageal cancers (GEC) have high mortality rates and the majority of patients present with advanced stage at diagnosis or succumb due to disease recurrence even after radical resection of the primary tumor. Biomarkers that can help optimize treatment strategy are thus highly desirable. The present study is a review of published data on ctDNA in GEC patients. We identified 25 studies in which tumor-specific genetic aberrations were investigated in plasma or serum and discuss these in relation to the methods applied for ctDNA analysis. The methods used for ctDNA detection greatly influence the sensitivity of the analysis and, therefore, the potential clinical applications. We found that studies of ctDNA in GEC, although limited in number, are promising for several applications such as genetic profiling of tumors and monitoring of disease progression. However, more studies are needed to establish if and how this analysis can be clinically implemented.

Quantitative Analysis of HER2 Amplification by Droplet Digital PCR in the Follow-Up of Gastric Cancer Patients Being Treated with Trastuzumab after Surgery

Background

Circulating tumor DNA (ctDNA) derived from tumors is a promising biomarker for monitoring tumor status and evaluating therapeutic effects and prognosis. We studied the plasma human epidermal growth factor receptor 2 (HER2) amplification in gastric cancer (GC) patients by droplet digital PCR (ddPCR) during therapy with trastuzumab.

Methods

A total of 12 patients were recruited after surgery. All patients received FOLFOX chemotherapy combined with trastuzumab as a treatment regimen. During the 12 months of the follow-up period, using elongation factor Tu GTP binding domain containing 2 (EFTUD2) as a reference gene, plasma HER2 to EFTUD2 ratios (the HER2 ratio) were determined for each patient every 2 months by ddPCR.

Results

The concordance rate of HER2 amplification examined in plasma and formalin-fixed paraffin-embedded (FFPE) samples with ddPCR was 81.4%, with a sensitivity of 76.5% and a specificity of 83.8%. Plasma HER2 ratios were correlated with the primary tumor size (p < 0.01). A significant decrease in the plasma HER2 ratio was found after two months of treatment (p < 0.0001). Nine patients experienced partial response, and three patients had stable disease. Seven patients had progressive disease (PD) during follow-up, and four of them had died. The median progression-free survival (PFS) was 9.8 months. For each patient who developed PD, the plasma HER2 ratio was approximately 2.3-4.1 times higher than the cut-off value at the time of PD, which was the highest during the whole follow-up period.

Conclusion

Longitudinal monitoring for the plasma HER2 ratio by ddPCR in the clinical courses of GC patients holds great promise for use as an indicator of tumor progression and treatment efficacy.

The Use of Circulating Tumor DNA for Prognosis of Gastrointestinal Cancers

Gastrointestinal cancers, including oesophageal, gastric and colorectal cancers (CRC) have high rates of disease recurrence despite curative resection. There are a number of recent studies that have investigated the use of circulating tumor DNA (ctDNA) for prognostic value in these cancers. We reviewed studies that had been published prior to March 2018 that assessed the prognostic values of ctDNA in patients with oesophageal and gastric cancers, gastrointestinal stromal tumors (GIST) and CRC. We identified 63 eligible clinical studies that focussed on recurrence and survival. Studies assessed investigated various ctDNA biomarkers in patients with different stages of cancer undergoing surgical resection, chemotherapy and no treatment. For oesophageal squamous cell carcinoma and oesophageal adenocarcinoma, methylation of certain genes such as APC and DAPK have been highlighted as promising biomarkers for prognostication, but these studies are limited and more comprehensive research is needed. Studies focusing on gastric cancer patients showed that methylation of ctDNA in SOX17 and APC were independently associated with poor survival. Two studies demonstrated an association between ctDNA and recurrence and survival in GIST patients, but more studies are needed for this type of gastrointestinal cancer. A large proportion of the literature was on CRC which identified both somatic mutations and DNA methylation biomarkers to determine prognosis. ctDNA biomarkers that identified somatic mutations were more effective if they were personalized based on mutations found in the primary tumor tissue, but ctDNA methylation studies identified various biomarkers that predicted increased risk of recurrence, poor disease free survival and overall survival. While the use of non-invasive ctDNA biomarkers for prognosis is promising, larger studies are needed to validate the clinical utility for optimizing treatment and surveillance strategies to reduce mortality from gastrointestinal cancers.

Preoperative Circulating Tumor DNA in Patients with Peritoneal Carcinomatosis is an Independent Predictor of Progression-Free Survival

BACKGROUND

Next-generation sequencing (NGS) is a useful tool for detecting genomic alterations in circulating tumor DNA (ctDNA). To date, most ctDNA tests have been performed on patients with widely metastatic disease. Patients with peritoneal carcinomatosis (metastases) present unique prognostic and therapeutic challenges. We therefore explored preoperative ctDNA in patients with peritoneal metastases undergoing surgery.

METHODS

Patients referred for surgical resection of peritoneal metastases underwent preoperative blood-derived ctDNA analysis (clinical-grade NGS [68-73 genes]). ctDNA was quantified as the percentage of altered circulating cell-free DNA (% cfDNA).

RESULTS

Eighty patients had ctDNA testing: 46 (57.5%) women; median age 55.5 years. The following diagnoses were included: 59 patients (73.8%), appendix cancer; 11 (13.8%), colorectal; five (6.3%), peritoneal mesothelioma; two (2.5%), small bowel; one (1.3%) each of cholangiocarcinoma, ovarian, and testicular cancer. Thirty-one patients (38.8%) had detectable preoperative ctDNA alterations, most frequently in the following genes: TP53 (25.8% of all alterations detected) and KRAS (11.3%). Among 15 patients with tissue DNA NGS, 33.3% also had ctDNA alterations (overall concordance = 96.7%). Patients with high ctDNA quantities (≥ 0.25% cfDNA, n = 25) had a shorter progression-free survival (PFS) than those with lower ctDNA quantities (n = 55; 7.8 vs. 15.0 months; hazard ratio 3.23, 95% confidence interval 1.43-7.28, p = 0.005 univariate, p = 0.044 multivariate).

CONCLUSIONS

A significant proportion of patients with peritoneal metastases referred for surgical intervention have detectable ctDNA alterations preoperatively. Patients with high levels of ctDNA have a worse prognosis independent of histologic grade.

Prognostic and predictive blood biomarkers in gastric cancer and the potential application of circulating tumor cells

Gastric cancer (GC), with its high incidence and mortality rates, is a highly fatal cancer that is common in East Asia particularly in China. Its recurrence and metastasis are the main causes of its poor prognosis. Circulating tumor cells (CTCs) or other blood biomarkers that are released into the circulating blood stream by tumors are thought to play a crucial role in the recurrence and metastasis of gastric cancer. Therefore, the detection of CTCs and other blood biomarkers has an important clinical significance; in fact, they can help predict the prognosis, assess the staging, monitor the therapeutic effects and determine the drug susceptibility. Recent research has identified many blood biomarkers in GC, such as various serum proteins, autoantibodies against tumor associated antigens, and cell-free DNAs. The analysis of CTCs and circulating cell-free tumor DNA (ctDNA) in the peripheral blood of patients with gastric cancer is called as liquid biopsy. These blood biomarkers provide the disease status for individuals and have clinical meaning. In this review, we focus on the recent scientific advances regarding CTCs and other blood biomarkers, and discuss their origins and clinical meaning.

Liquid biopsy provides new insights into gastric cancer

Liquid biopsies have great promise for precision medicine as they provide information about primary and metastatic tumors via a minimally invasive method. In gastric cancer patients, a large number of blood-based biomarkers have been reported for their potential role in clinical practice for screening, early diagnosis, prognostic evaluation, recurrence monitoring and therapeutic efficiency follow-up. This current review focuses on blood liquid biopsies' role and their clinical implications in gastric cancer patients, with an emphasis on circulating tumor cells (CTCs), circulating tumor DNA (ctDNA) and circulating non-coding RNAs (ncRNAs). We also provide a brief discussion of the potential and limitations of liquid biopsies use and their future use in the routine clinical care of gastric cancer.

Clinical relevance of cell-free DNA in gastrointestinal tract malignancy

BACKGROUND

Cell-free DNA (cfDNA) extracted from blood has become a clinically feasible biomarker in various types of cancer. However, the clinical significance of cfDNA in gastrointestinal (GI) tract cancer among Asian populations requires further investigation.

RESULTS

The median cfDNA copy number was highest in esophageal cancer, followed by colorectal cancer and gastric cancer, which were all significantly higher than those of healthy individuals. The cfDNA levels were higher in GI tract cancer, followed by those in carcinoma in situ and then healthy individuals (P = 0.019). During the postoperative surveillance, the cfDNA level tended to be more sensitive than the carcinoembryonic antigen level in predicting recurrence. For recurrent gastric cancer, a persistently high cfDNA level and an increasing trend was observed after surgery. For stage IV colorectal cancer, dynamic changes in the cfDNA level were correlated with the responses to chemotherapy and surgery.

MATERIALS AND METHODS

Blood samples were collected from 95 healthy individuals and from 855 patients diagnosed with GI tract malignancy, including 98 with esophageal cancer, 428 with stomach cancer, 329 with colorectal cancer and 30 with carcinoma in situ. The copy numbers of extracted cfDNA were analyzed and compared among the different types of GI cancers.

CONCLUSIONS

The cfDNA level can serve as a feasible biomarker for detecting tumors in GI tract cancer. The cfDNA level may play a role in predicting tumor responses to chemotherapy and surgery in colorectal cancer; tumor recurrence should be considered in gastric cancer with a persistently high cfDNA level after surgery.

Clinical value of ctDNA in upper-GI cancers: A systematic review and meta-analysis

BACKGROUND

The recent expanding technical possibilities to detect tumor derived mutations in blood, so-called circulating tumor DNA (ctDNA), has rapidly increased the interest in liquid biopsies. This review and meta-analysis explores the clinical value of ctDNA in malignancies of the upper gastro-intestinal tract.

METHODS

PubMed, Cochrane and Embase databases were searched to identify studies reporting the diagnostic, prognostic or predictive value of ctDNA in patients with esophageal, gastric and pancreatic cancer, until January 2017. The diagnostic accuracy and, using random-effect pair-wise meta-analyses, the prognostic value of ctDNA was assessed.

RESULTS

A total of 34 studies met the inclusion criteria. For esophageal and gastric cancer, amplification of oncogenes in blood, such as HER2 and MYC, can be relevant for diagnostic purposes, and to predict treatment response in certain patient subpopulations. Given the limited number of studies assessing the role of ctDNA in esophageal and gastric cancer, the meta-analysis estimated the diagnostic accuracy and predictive value of ctDNA in pancreatic cancer only (n=10). The pooled sensitivity and specificity of ctDNA as a diagnostic tool in pancreatic cancer were 28% and 95%, respectively. Patients with pancreatic cancer and detectable ctDNA demonstrated a worse overall survival compared to patients with undetectable ctDNA (HR 1.92, 95% confidence interval (CI) 1.15-3.22, p=0.01).

CONCLUSION

The presence of ctDNA is significantly associated with a poor prognosis in patients with pancreatic cancer. The use of ctDNA in clinical practice is promising, although standardization of sequencing techniques and further development of high-sensitive detection methods is needed.

Dynamic tracing for epidermal growth factor receptor mutations in urinary circulating DNA in gastric cancer patients

The mutations of epidermal growth factor receptor are detected in gastric cancer, indicating its suitability as a target for receptor tyrosine kinase inhibitors, as well as a marker for clinical outcome of chemotherapeutic treatments. However, extraction of quality tumor tissue for molecular processes remains challenging. Here, we aimed to examine the clinical relevance of urinary cell-free DNA as an alternative tumor material source used specifically for monitoring epidermal growth factor receptor mutations. Therefore, 120 gastric cancer patients with epidermal growth factor receptor mutations and 100 healthy controls were recruited for the study. The gastric patients also received epidermal growth factor receptor inhibitor treatment for a serial monitoring study. Paired primary tumor specimens were obtained with blood and urine samples, which were taken at a 1-month interval for a duration of 12 months. We found that urinary cell-free DNA yielded a close agreement of 92% on epidermal growth factor receptor mutation status when compared to primary tissue at baseline, and of 99% epidermal growth factor receptor mutation status when compared to plasma samples at different time points. Thus, our data suggest that urinary cell-free DNA may be a reliable source for screening and monitoring epidermal growth factor receptor mutations in the primary gastric cancer.

Gastric cancer - clinical and epidemiological aspects

Gastric cancer (GC) ranks fifth for cancer incidence and second for cancer deaths. Epidemiological data showed that survivors of Hodgkin's lymphoma and patients with pernicious anemia etiologically linked to autoimmune gastritis are at increased risk of GC. Screening of patients with autoimmune thyroid disease by means of pepsinogen (PG) I and PG I/II detected autoimmune gastritis with oxyntic gastric atrophy in one of four patients and may be recommended for GC prevention purposes. The International Agency for Research on Cancer reported a positive association between consumption of processed meet and increased GC risk. A new GC risk prediction model based on biological markers, age, gender, smoking status, family history of GC, and consumption of highly salted food showed good predictive performance, and might prompt individuals to modify their lifestyle habits, attend regular check-up visits or participate in screening programs. A novel GC classification based on gene expression of primary resected cancers correlated with clinicopathological features. Noncoding RNA for GC screening remains the focus of multiple studies. Patients with early GC undergoing endoscopic resection are more likely to develop metachronous lesions than patients undergoing surgery and endoscopic surveillance is warranted in this special cohort. The addition of gastrectomy to chemotherapy did not improve survival of patients with advanced GC and a single noncurable factor. Apatinib, a novel oral vascular endothelial growth factor receptor 2 tyrosine kinase inhibitor, improved the median overall survival of patients with advanced GC and progressive disease after two or more lines of prior chemotherapy of nearly 3 months.