Detection of Micrometastases in Peritoneal Washings of Gastric Cancer Patients By Quantitative Real Time Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR)
Kimberly M. Dalal*1,2, Yanghee Woo2, Charles Galanis2, Mithat Gonen3, Yuman Fong2, Daniel G. Coit2
1Surgery, David Grant USAF Medical Center, Travis AFB, CA; 2Surgery, Memorial Sloan-Kettering Cancer Center, New York, NY; 3Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, NY
Introduction: Gastric cancer patients with positive (+) peritoneal cytology have a prognosis similar to stage IV patients. We studied the ability of a quantitative RT-PCR assay to detect micrometastases in patients undergoing staging laparoscopy for gastric cancer.
Methods: Peritoneal washes were obtained prospectively from 30 consecutive consented patients with gastric adenocarcinoma undergoing laparoscopy for staging and 6 patients undergoing laparoscopy for benign disease (negative controls). Half of each sample was sent to pathology for cytologic examination; half underwent RT-PCR analysis for tumor markers. Carcinoembryonic antigen (CEA), cytokeratin 20 (CK20), survivin, and muc2 mRNA levels were quantified and normalized to 18s mRNA. Positive controls were patients with (+) cytology or visible peritoneal metastases. The threshold for cycle amplification was <36 cycles. A tumor marker was (+) if the ratio of tumor marker mRNA/18S mRNA was >1.5. Markers and their combinations were evaluated on the basis of their distance, or deviance, from the ideal marker (ie, 100% sensitive and specific).
Results: The median age of the cohort was 62. Seventeen patients (47%) were female. Pathologic stage for gastric cancer patients was: stage IB-7 (23%); stage II-6 (20%); stage III-14 (47%); stage IV-3 (10%). The five cytology (+) patients were stage II-1; stage III-1; stage IV-3. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value were highest for CEA, CEA+CK20, CEA+MUC2, CEA+CK20+MUC2 (Table). As CEA alone had the smallest deviance, other markers did not provide additional benefit. Survivin had a sensitivity of 100% but a PPV of only 31%.
Conclusions: RT-PCR using a panel of tumor markers, including CEA, was as sensitive as cytology with comparable specificity, PPV, and NPV. The clinical significance of “false positive” overexpression of CEA, survivin, or CK20 remains to be defined. RT-PCR could represent a more sensitive method for detection of subclinical peritoneal tumor dissemination, and this may be useful in improving selection of patients for operative management and clinical trials.
| Tumor Marker mRNA | True Positive | True Negative | False Positive | False Negative | Sensitivity TP/(TP+FN) | Specificity TN/(FP+TN) | Positive Predictive Value TP/(TP+FP) | Negative Predictive Value TN/(FN+TN) | Deviance |
| CEA | 5 | 26 | 4 | 0 | 1.00 | 0.87 | 056 | 1.00 | 0.13 |
| CK20 | 3 | 27 | 2 | 2 | 0.60 | 0.93 | 0.60 | 0.93 | 0.41 |
| Survivin | 4 | 20 | 9 | 0 | 1.00 | 0.69 | 0.31 | 1.00 | 0.31 |
| MUC2 | 2 | 27 | 0 | 1 | 0.67 | 1.00 | 1.00 | 0.96 | 0.33 |
| CEA+CK20 | 5 | 26 | 4 | 0 | 1.00 | 0.87 | 0.56 | 1.00 | 0.13 |
| CEA+MUC2 | 4 | 23 | 4 | 0 | 1.00 | 0.85 | 0.50 | 1.00 | 0.15 |
| CEA+CK20+MUC2 | 4 | 23 | 4 | 0 | 1.00 | 0.85 | 0.50 | 1.00 | 0.15 |
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