Pancreas Cyst Fluid KRAS Mutation Is an Accurate Marker for the Diagnosis of a Mucinous Cyst: 308

Introduction: The presence of a KRAS mutation in cyst fluid has been suggested as a highly specific test for the classification of a cyst as mucinous. However, the number of clinical studies using histology as the diagnostic ‘gold standard’ is small. This study aimed to assess the accuracy of the testing of KRAS mutation together with cyst fluid CEA for differentiation mucinous from non-mucinous cysts. Methods: KRAS mutation testing was performed on all cyst fluid testing at MGH over the past 8 years. KRAS mutation was determined by using SNaPshot (Life technologies) genotyping system. Fluid CEA level was measured using specific radioimmunoassay (Abbott Diagnostics). Cytological analyses were carried out by an expert cytologist. The classification of cyst type was based on either histology in patients who underwent surgery or clinical evaluation with cross-sectional imaging, EUS findings, and cytology. At least 2 experts classified the cyst based on clinical data. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of KRAS, CEA, and their combination for the diagnosis of a mucinous cyst were calculated from a prospectively maintained, IRBapproved database. Results: A total of 281 patients were examined in the analysis. The cyst classification was made with the results of surgical histology in 50 patients and with clinical evaluation in 231 patients. The classifications of cysts were intraductal papillary neoplasm (n=181), mucinous cystic neoplasm (n=19), pseudocyst (n=40), serous cyst adenoma (n=31), endocrine cyst (n=9), and lymphoepithelial cyst (n=1). The test (KRAS and CEA) accuracy (%) were determined according to mucinous and non-mucinous classification and summarized in the table. KRAS and CEA (>192 ng/mL) were found to be highly specific for the diagnosis of a mucinous cyst. However, the sensitivity of the tests was limited. The combination of both tests improved the sensitivity and diagnostic accuracy to 77% and 83%, respectively. The diagnostic accuracy of a combination of KRAS-CEA was significantly better than KRAS (p<0.039) or CEA (p<0.002) alone. Conclusion: The addition of KRAS mutation testingimproves the accuracy of diagnosis of mucinous cysts.Table 1