Abstract B22: High prevalence of TSC2 germline missense mutations in nontuberous sclerosis patients with gastroenteropancreatic neuroendocrine neoplasia
Authors: Linck Rudinei Diogo Marques , Asprino Paula Fontes , Cesar Jônatas Eduardo da Silva , Freitas Florêncio Porto , Koyama Fernanda Christtanini , Riechelmann Rachel Simões Pimenta , Galante Pedro Alexandre Favoretto , Costa Frederico Perego , Hoff Paulo Marcelo Gehm , Meyer Diogo , Camargo Anamaria Aranha , Sabbaga Jorge 
Published: May 2019

Abstract
Background: Neuroendocrine neoplasias (NENs) are sporadic diseases, with only a few cases occurring in patients with predisposing syndromes, such as multiple endocrine neoplasia type 1 and type 2, von Hippel-Lindau disease, neurofibromatosis, and tuberous sclerosis. Nevertheless, epidemiologic researches have demonstrated that, even for previously healthy people, there is a higher risk for developing gastroenteropancreatic (GEP) NENs when a relative is affected by these neoplasms. The molecular basis to explain this familial pattern is, however, still unrecognized. We examined germline genes of GEP NEN nonsyndromic patients and looked for mutations that could justify this genetic susceptibility.
Methods: Patients with GEP NEN who were in medical care between March to November 2015 at Hospital Sírio-Libanês or Instituto do Câncer do Estado de São Paulo (both in São Paulo, Brazil) were invited to participate of the study. We excluded patients with previously known mutation in any gene surveyed in this study (MEN1, RET, VHL, NF1, TSC1, and TSC2). All participating patients signed the written informed consent form. Targeted next-generation sequencing of the coding region of the 6 genes which are associated with NEN physiopathology was performed in germline DNA. Only mutations with damaging impact by SIFT or PolyPhen2 functional predictors; with minor allele frequency (MAF) lower than 0.1% and with confirmed analysis by Sanger sequencing, were considered for the results. Enrichment of mutations in the evaluated genes in GEP NEN patients was verified by Fisher's exact test, contrasting the results of the GEP NEN group with the ExAC populational database.
Results: Ninety-three patients were included in the study (54.8% males) with the median age at diagnosis of 52 years. No patients had clinical phenotype of any syndromes related to NENs predisposition. The majority of patients had neoplasia grades 1 and 2 (38.7% and 41.9%), with primary site in pancreas (44.1%) or small bowel (35.5%) and were not associated with functional syndrome (74.2%). Eight patients (8.6%) have germline missense mutations in the TSC2 gene, and 1 patient (1.1%) in RET. There were no clear differences on age at diagnosis, neoplasia differentiation, site of the primary tumor, or diagnosis of functional syndrome when comparing patients with or without mutations. Populational analysis have shown an odds ratio of 3.8 (IC95% 1.42-7.42; p-value=0.004) for detecting TSC2 mutation in GEP NEN patients comparing with ExAC database. All mutations detected in the TSC2 are not diagnostic for tuberous sclerosis by consensus criteria. No association was seen in RET mutation (OR=1.00).
Conclusion: GEP NEN patients without clinical phenotype of any syndrome related to NENs susceptibility are significantly enriched for germline damaging missense mutation in the TSC2 gene. There is no enrichment of mutations in other evaluated genes. Taking into account the increasingly consistent evidence about hereditary predisposition in GEP NEN, as well as the already established relationship of truncated tuberin protein with predisposition of NENs, these findings strongly suggest that TSC2 damaging missense mutation is implicated in the genesis of GEP NEN in some nonsyndromic patients. Although these mutations are not associated with classical phenotype of tuberous sclerosis, this condition could be considered a new feature of a mild tuberous sclerosis.
Funding: This research was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and by Ludwig Institute for Cancer Research São Paulo.
Citation Format: Rudinei Diogo Marques Linck, Paula Fontes Asprino, Jônatas Eduardo da Silva Cesar, Florêncio Porto Freitas, Fernanda Christtanini Koyama, Rachel Simões Pimenta Riechelmann, Pedro Alexandre Favoretto Galante, Frederico Perego Costa, Paulo Marcelo Gehm Hoff, Diogo Meyer, Anamaria Aranha Camargo, Jorge Sabbaga. High prevalence of TSC2 germline missense mutations in nontuberous sclerosis patients with gastroenteropancreatic neuroendocrine neoplasia [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr B22.