Pyrosequencing Identifies GNAS R201 “Hotspot” Mutations in Cytology Specimens Obtained from Intraductal Papillary Mucinous Neoplasms and Associated Adenocarcinomas: An Adjunct Tool for Molecular Diagnosis of Pancreatic Cystic Neoplasms
Scott Robertson, Mitsuro Kanda, Yoshihiko Sadakari, Ralph Hruban, Michael Goggins, Armanda Tatsas, Anirban Maitra. Johns Hopkins Hospital, Baltimore, MD
Background: Intraductal papillary mucinous neoplasms are bona fide precursor lesions of pancreatic ductal adenocarcinomas (PDAC). Currently, endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is used to obtain cyst fluid for evaluation. EUS-FNA cytology, however, can frequently be non-diagnostic or equivocal. Molecular analyses of IPMNs have identified activating mutations of GNAS at codon R201 in ∼66% of lesions (including IPMN-associated PDACs), while this mutation is typically absent in other pancreatic cystic neoplasms and in non-IPMN associated PDACs. Assessment of GNAS mutations in EUS-FNA material could potentially be a valuable adjunct in the assessment of pancreatic cysts.
Design: We have previously reported GNAS mutational status in a series of ∼100 IPMN-associated cyst fluid samples obtained at the time of surgical resection (Wu et al, Sci Transl Med 2011); in nine of these IPMNs, sufficient pre-operative EUS-FNA samples were available for DNA extraction and sequencing. Cytology specimens from entities not expected to harbor GNAS mutations, specifically, pancreatic neuroendocrine tumors (1), solid-pseudopapillary neoplasms (2), and PDACs not associated with an IPMN (3), were utilized as controls. From these preparations, DNA was extracted and pyrosequencing was used to detect GNAS mutations.
Results: Mutations in GNAS were detected in 7 out of 9 (78%) cytology samples of IPMNs, including non-invasive IPMNs (2/4, 50%) and in IPMN-associated PDACs (5/5, 100%). GNAS mutations were not detected in the remaining 6 samples from non-IPMN pancreatic lesions. Possibly as a manifestation of cyst multifocality, we found discordance in 5 of 9 cases when we compared the mutational status of GNAS in the cytology material with that of the cyst fluid obtained at the time of surgery. In the majority of these cases (4/5, 80%), GNAS mutations were detected in the cytology material but not in cyst aspirated at surgery. In one case, the cytology material contained only wild type sequence while GNAS mutant sequence was detected in the cyst fluid.
Conclusions: Pyrosequencing can detect GNAS mutations in routine cytology preparations from IPMNs and IPMN-associated PDACs. Cytology specimens might provide an added degree of sensitivity over acellular cyst fluid samples in the detection of mutant DNA sequence. This method could provide a valuable adjunct by allowing more accurate triage of cystic pancreatic neoplasms pre-operatively.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 135, Wednesday Afternoon