Clinical Benefits of KRAS/GNAS Gene Mutation Analysis in Addition to Morphology and Conventional Cyst Fluid Testing in Differentiating Pancreatic Cysts

Abstract

Objectives: Pancreatic cystic lesions (PCLs) are increasingly detected due to the widespread use of imaging techniques. The identification of pancreatic mucinous cysts is especially important since these carry a risk of malignant transformation and require follow-up or surgical resection. The aim of this study was to determine the diagnostic yield of the molecular analysis of K-RAS (Kirsten RAt Sarcoma virus) and GNAS (Guanine Nucleotide-binding protein, Alpha Stimulating protein activity) gene mutations in pancreatic cyst fluid (PCF) obtained by endoscopic ultrasound (EUS)-guided fine needle aspiration (FNA). Methods: In this prospective trial, we assessed the sensitivity, specificity, and positive and negative predictive values of K-RAS and GNAS mutation analysis in differentiating mucinous versus non-mucinous cysts and the subsequent impact on decision-making in daily clinical practice. The reference standard used comprised the combination of morphology on cross-sectional imaging and EUS, string sign, cyst fluid cytology, intracystic carcinoembryonic antigen (CEA), and glucose levels, with subsequent correlation of surgical pathology in resected cases. Fluid samples of 47 cysts obtained by EUS-FNA over a 39-month period were analyzed. Mutation analysis of KRAS (exon 2) was performed in all cases, and additionally, GNAS (exon 8) in 28 cases using Sanger sequencing. Results: 33 out of 47 PCLs were classified as mucinous cysts and 14 as non-mucinous cysts defined using conventional standards, including morphological characteristics, string-sign, cytology, cyst fluid testing, and histology in resected cases. Of these 33 mucinous cysts, KRAS mutation was detected in 14 samples. A further 23 mucinous lesions were additionally tested for GNAS mutation, which was detected in 10 of the 23 cysts. A 42.4% sensitivity for KRAS and 43.5% for GNAS mutation analysis was calculated, with a specificity of 92.9% and 100%, respectively, for detecting mucinous lesions. The clinical management was altered through the genetic testing results in one single case. Conclusions: In this cohort, K-RAS and GNAS mutational analysis in cyst fluid did not improve the detection of mucinous pancreatic cysts significantly after conventional testing. However, the method may be useful due to its high specificity in uncertain cases.

Keywords: GNAS; KRAS; intracystic CEA; intracystic glucose; mutation analysis; pancreatic cystic neoplasm.

Figure 1

Diagnostic strategy.