Observational Study
Copyright ©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastrointest Oncol. Sep 15, 2020; 12(9): 1056-1064
Published online Sep 15, 2020. doi: 10.4251/wjgo.v12.i9.1056
Methylation changes at the GNAS imprinted locus in pancreatic cystic neoplasms are important for the diagnosis of malignant cysts
Sandra Faias, Marlene Duarte, Luísa Pereira, Paula Chaves, Marília Cravo, Antonio Dias Pereira, Cristina Albuquerque
Sandra Faias, Antonio Dias Pereira, Department of Gastroenterology, Instituto Português de Oncologia de Lisboa Francisco Gentil, EPE, Lisboa 1099-023, Portugal
Sandra Faias, Paula Chaves, Faculty of Health Sciences, University of Beira Interior, Covilhã 6200-506, Portugal
Marlene Duarte, Cristina Albuquerque, Unidade de Investigação em Patobiologia Molecular (UIPM), Instituto Português de Oncologia de Lisboa Francisco Gentil, EPE, Lisboa 1099-023, Portugal
Luísa Pereira, Centro de Matemática e Aplicações (CMA-UBI), Universidade da Beira Interior, Covilhã 6200-506, Portugal
Paula Chaves, Department of Pathology, Instituto Português de Oncologia de Lisboa Francisco Gentil, EPE, Lisboa 1099-023, Portugal
Marília Cravo, Department of Gastroenterology, Hospital Beatriz Ângelo, Loures 2674-514, Portugal
Author contributions: All authors have contributed to the paper concept and design and agreed on the final content of the manuscript; Faias S, Duarte M, and Albuquerque C acquired and interpreted the data; Pereira L performed the statistical analysis; Faias S, Pereira L, Chaves P, Cravo M, and Albuquerque C drafted the manuscript under the supervision of both senior authors, Albuquerque C and Pereira AD; all authors critically revised the manuscript and approved the final version of the manuscript.
Supported by a Research Grant from Sociedade Portuguesa de Endoscopia Digestiva in 2018.
Institutional review board statement: The study was approved by the Ethics Committee and Institutional Scientific Board (UIC/1143).
Informed consent statement: All patients gave informed consent.
Conflict-of-interest statement: The authors have no conflicts of interest to disclose.
Data sharing statement: No additional data are available.
STROBE statement: Guidelines of STROBE statement have been adopted.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Corresponding author: Sandra Faias, MD, Attending Doctor, Research Fellow, Department of Gastroenterology, Instituto Português de Oncologia de Lisboa Francisco Gentil, EPE, Rua Prof Lima Basto, Lisboa 1099-023, Portugal. sandrarfaias@hotmail.com
Received: April 15, 2020
Peer-review started: April 15, 2020
First decision: July 5, 2020
Revised: July 18, 2020
Accepted: August 1, 2020
Article in press: August 1, 2020
Published online: September 15, 2020
ARTICLE HIGHLIGHTS
Research background

Pancreatic cystic lesions (PCLs) constitute a clinical dilemma due to indeterminate risk of malignancy. Intraductal papillary mucinous neoplasms (IPMNs) and mucinous cystic neoplasms are cystic precursors of pancreatic ductal adenocarcinoma (PDAC), possibly allowing early diagnosis. Somatic mutations in GNAS are characteristic of IPMNs, but their role in carcinogenesis is unclear. GNAS is a complex imprinted locus that encodes the α-subunit of the stimulatory heterotrimeric G protein (Gsα), an ubiquitous signaling protein. This locus encodes four monoallelic (NESP55, AS, XL, 1A) and one biallelic (Gsα) transcript(s), due to differentially methylated regions (DMRs) in paternal and maternal alleles, denominated imprinting. Paternal methylation of NESP55 and maternal methylation of AS, XL, and 1A lead, respectively, to maternal and paternal allele expressions, with Gsα biallelically expressed in most tissues, due to absent methylation.

Research motivation

GNAS somatic mutations are characteristic of IPMNs, although epigenetic alterations in the GNAS locus have not been previously evaluated in PCLs. Methylation of DMRs at the GNAS locus may occur at the somatic level and modulate Gsα expression.

Research objectives

In this study, we evaluate if methylation changes in DMRs at the GNAS locus could contribute to tumor progression of PCLs.

Research methods

We performed a longitudinal cohort study of PCLs with GNAS locus methylation analysis performed in PCF samples obtained by endoscopic ultrasound with fine needle aspiration.

Research results

Fifty-two PCF samples obtained by endoscopic ultrasound with fine needle aspiration and previously characterized for KRAS and GNAS mutations were studied. The final diagnoses were surgical (11) and clinicopathological (41), including 30 benign cysts, 14 pre-malignant cyst, and eight malignant cysts. Methylation changes at NESP55, GNASAS, GNAS1A, and especially GNASXL were more frequent in malignant cysts and were useful for their diagnosis. A combined variable defined as “GNAS locus methylation changes” was significantly associated with malignancy (6/8 malignant cysts and only 2/20 benign cysts) and improved classification. Hypermethylation in both maternally (NESP55) and paternally (GNASXL) derived promoters was found in 3/3 PDACs.

Research conclusions

This is the first study to identify methylation changes in the GNAS locus that improved the diagnosis of malignant PCs and suggest a role in progression to PDAC.

Research perspectives

Although the small sample size and lack of validation in an independent sample are significant limits regarding the present study, our pilot data may be the basis for exploring GNAS methylation in larger, well-characterized sets of samples. As methylation status may impact gene expression, additional evaluation of GNAS transcripts in PCF may elucidate their function in pancreatic cystic neoplasms.