Activation of the RAS pathway through uncommonBRAFmutations in mucinous pancreatic cysts withoutKRASmutation

Diagnostic testing of pancreatic cyst fluid obtained by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) has traditionally utilized elevated carcinoembryonic antigen (CEA) (>= 192 ng/ml) and cytomorphologic examination to differentiate premalignant mucinous from benign pancreatic cystic lesions (PCLs). Molecular testing forKRAS/GNASmutations has been shown to improve accuracy of detecting mucinous PCLs. Using a targeted next-generation sequencing (NGS) panel, we assess the status of PCL-associated mutations to improve understanding of the key diagnostic variables. Molecular analysis of cyst fluid was performed on 108 PCLs that had concurrent CEA and/or cytological analysis. A 48-gene NGS assay was utilized, which included genes commonly mutated in mucinous PCLs such asGNAS, KRAS, CDKN2A, andTP53.KRASand/orGNASmutations were seen in 59 of 68 (86.8%) cases with multimodality diagnosis of a mucinous PCL. Among 31 patients where surgical histopathology was available, the sensitivity, specificity, and diagnostic accuracy of NGS for the diagnosis of mucinous PCL was 88.5%, 100%, and 90.3%, respectively. Cytology with mucinous/atypical findings were found in only 29 of 62 cases (46.8%), with fluid CEA elevated in 33 of 58 cases (56.9%). MultipleKRASmutations at different variant allele frequencies were seen in seven cases favoring multiclonal patterns, with six of them showing at least two separate PCLs by imaging. Among the 6 of 10 cases withGNAS + /KRAS- results, uncommon, non-V600E exon 11/15 hotspotBRAFmutations were identified. The expected high degree of accuracy of NGS detection ofKRASand/orGNASmutations for mucinous-PCLs, as compared with CEA and cytological examination, was demonstrated. MultipleKRASmutations correlated with multifocal cysts demonstrated by radiology. In IPMNs that lackedKRASmutations, the concurringBRAFmutations withGNASmutations supports an alternate mechanism of activation in the Ras pathway.