Biomarkers are measurable indicators of a biological state. As our understanding of diseases meliorates, it is generally accepted that early diagnosis renders the best chance to cure a disease. In the context of proteomics, the discovery phase of identifying bonafide biomarkers and the ensuing validation phase involving large cohort of patient samples are impeded by the complexity of bodily fluid samples. High abundant proteins found in blood plasma make it difficult for the detection of low abundant proteins that may be potential biomarkers. Extracellular vesicles (EVs) have reignited interest in the field of biomarker discovery. EVs contain a tissue-type signature wherein a rich cargo of proteins and RNA are selectively packaged. In addition, as EVs are membranous structures, the luminal contents are protected from degradation by extracellular proteases and are highly stable in storage conditions. Interestingly, an appealing feature of EV-based biomarker analysis is the significant reduction in the sample complexity compared to whole bodily fluids. With these prescribed attributes, which are the rate-limiting factors of traditional biomarker analysis, there is immense potential for the use of EVs for biomarker detection in clinical settings. This review will discuss the current issues with biomarker analysis and the potential use of EVs as reservoirs of disease biomarkers.

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Exosomes in bodily fluids are a highly stable resource of disease biomarkers.

The aim of this review was to evaluate the clinical significance of serum tumor markers, particularly CEA, CA19-9, and CA72-4, in patients with gastric cancer. A systematic literature search was performed using PubMed/MEDLINE with the keywords “gastric cancer” and “tumor marker,” to select 4,925 relevant reports published before the end of November 2012. A total of 187 publications contained data for CEA and CA19-9, and 19 publications contained data related to all three tumor markers. The positive rates were 21.1 % for CEA, 27.8 % for CA19-9, and 30.0 % for CA72-4. These three markers were significantly associated with tumor stage and patient survival. Serum markers are not useful for early cancer, but they are useful for detecting recurrence and distant metastasis, predicting patient survival, and monitoring after surgery. Tumor marker monitoring may be useful for patients after surgery because the positive conversion of tumor markers usually occurs 2–3 months before imaging abnormalities. Among other tumor markers, alpha-fetoprotein (AFP) is useful for detecting and predicting liver metastases. Moreover, CA125 and sialyl Tn antigens (STN) are useful for detecting peritoneal metastases. Although no prospective trial has yet been completed to evaluate the clinical significance of these serum markers, this literature survey suggests that combinations of CEA, CA19-9, and CA72-4 are the most effective ways for staging before surgery or chemotherapy. In particular, monitoring tumor markers that were elevated before surgery or chemotherapy could be useful for detection of recurrence or evaluation of the response.

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Clinical significance of serum tumor markers for gastric cancer: a systematic review of literature by the Task Force of the Japanese Gastric Cancer Association

Background Obstructive jaundice is frequently associated with false CA19-9 elevation in benign conditions. The diagnostic accuracy of this tumor marker was evaluated in the present longitudinal study. Methods In 128 patients admitted for obstructive jaundice (87 with pancreato-biliary malignancy and 41 benign disease) serum CA19-9 was measured. Statistical analysis of marker levels obtained before and after endoscopic biliary drainage was performed in 60 patients. Results Elevated CA19-9 levels (>37 U/mL) were found in 61% of benign cases and 86% of malignancies. After biliary drainage, decrease of serum CA19-9 was observed in 19 of 38 malignant cases and in almost all benign cases (Wilcoxon matched pairs test: P = .207 and P Conclusions In the presence of successfully drained obstructive jaundice, CA19-9 serum levels that remain unchanged or measure more than 90 U/mL are strongly indicative of a malignant cause of obstruction. However, the real clinical utility of this marker remains controversial.

CA19-9 serum levels in obstructive jaundice: clinical value in benign and malignant conditions

Background: Updated National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for the use of tumor markers in the clinic have been developed.

Methods: Published reports relevant to use of tumor markers for 4 cancer sites—liver, bladder, cervical, and gastric—were critically reviewed.

Results: α-Fetoprotein (AFP) may be used in conjunction with abdominal ultrasound for early detection of hepatocellular carcinoma (HCC) in patients with chronic hepatitis or cirrhosis associated with hepatitis B or C virus infection. AFP concentrations >200 μg/L in cirrhotic patients with typical hypervascular lesions >2 cm in size are consistent with HCC. After a diagnosis of HCC, posttreatment monitoring with AFP is recommended as an adjunct to imaging, especially in the absence of measurable disease.

Although several urine markers have been proposed for bladder cancer, none at present can replace routine cystoscopy and cytology in the management of patients with this malignancy. Some may, however, be used as complementary adjuncts to direct more effective use of clinical procedures.

Although carcinoembryonic antigen and CA 19-9 have been proposed for use gastric cancer and squamous cell carcinoma antigen for use in cervical cancer, none of these markers can currently be recommended for routine clinical use.

Conclusions: Implementation of these recommendations should encourage optimal use of tumor markers for patients with liver, bladder, cervical, or gastric cancers.

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National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for Use of Tumor Markers in Liver, Bladder, Cervical, and Gastric Cancers

Background: The aim of this longitudinal study was to evaluate the effectiveness of the serum tumor markers CEA, CA 19-9, and CA 72-4 in the early diagnosis of recurrence of gastric cancer. Methods: One hundred and thirty-three patients who had undergone potentially curative surgery were considered. Serum samples were obtained preoperatively, 1 week after surgery, and at every follow-up examination. Mean follow-up time for the entire patient population was 41 ± 33 months, and 71 ± 27 months for patients classified as disease-free. Results: Preoperative positivity was 16% for CEA, 35% for CA 19-9, and 20% for CA 72-4. Recurrence of disease was found in 75 patients (56%). Marker sensitivity in recurrent cases was 44% for CEA, 56% for CA 19-9, and 51% for CA 72-4; the combined use of the three markers increased sensitivity to 87%, which reached 100% in patients with positive preoperative levels. Marker specificity, evaluated in 58 disease-free patients, was 79% for CEA, 74% for CA 19-9, and 97% for CA 72-4. Conclusions: The combined assay of CEA, CA 19-9, and CA 72-4 may be useful for early diagnosis of recurrence of gastric cancer; however, only CA 72-4 positivity should be considered a specific predictor of tumor recurrence.

Clinical utility of CEA, CA 19-9, and CA 72-4 in the follow-up of patients with resectable gastric cancer

The prognostic value of preoperative serum levels of CEA, CA 19-9 and CA 72-4 tumor markers was investigated in 153 patients resected for gastric cancer. The positivity rates for CEA, CA 19-9 and CA 7

Angelo Messano

Papers

Prognostic significance of CEA, CA 19-9 and CA 72-4 preoperative serum levels in gastric carcinoma.