Background: In adult GISTs are frequently sporadic, while rarely GISTs are linked to Carney Triad and Carney-Stratakis Syndrome and NF1. GISTs with second primary tumors are reported in 4-33% of patients in literature and genetic counseling is suggested to explore an underlying germline mutations pathway. Methods: In our Academic Hospital Centre (EURACAN member) in Florence, Italy, we are following patients with GIST and multiple primary tumors with genetic counseling (72 GISTs with second tumors/185 patients with GIST) and germline analysis of the following genetic panel is performed as clinically indicated: BRCA1, BRCA2, MUTYH, MLH1, MSH2, MSH6, CDH1, ATM, TP53, PTEN, CHECK2, PALB2, BARD1, BRIP1, BLM, RAD51C, RAD51D, XRCC2, PMS2, MRE11A, RAD50, NBN, FAM175A, EPKAM, TSK1, MEN1 by sequencing analysis with Illumina MiSeq by kit multiplicom BRCA Hereditary cancer Mastr plus, and bioinformatic analysis by software SOPHIADDM (Sophia genetics) for point genetic alterations of BRCA1 NM_007294.3, BRCA2 NM_000059.3, MUTYH NM_000249, MSH2 NM_000251, MSH6 NM_000179, CDH1 NM_00444360, ATM NM_000051, TP53 NM_000546, PTEN NM_000314, CHEK2 NM_001005735, PALB2 NM_024675, BARD1 NM_000465, BRIP1 NM_032043, BLM NM_000057, RAD51C NM_002876, RAD51D NM_001142571, XRCC2 NM_005431, PMS2 NM_000535, MRE11A NM_005590, RAD50 NM_006732, NBN NM_002485, FAM175A NM_139076, EPCAM NM_002354, STK1 NM_000455, MEN1 NM_000244 and MLPA (Multiplex Ligation-dependent Probe Amplification) test analysis for patients with kit P087-BRCA1,P045-BRCA2(CHEK2, P248-MLH1-MSH2, P003-MLH1/MSH2, P072-MSH6-MUTYH (MRC-Holland). Results: In 3 patients germline mutations have been observed: 1 patient showed the c.1192dupG, p.(Ala398Glyfs*19) pathogenic mutation in exon 7 of MSH2 gene, confirmed by Sanger Sequencing, 1 patient showed c.565-?_1130+?del mutation consisting in heterozygous 3-4-5-6 exons deletion of MSH2 gene, confirmed by MLPA analysis, and in 1 patient the following ATM alteration has been identified in heterozygosis: ATM c.5319+2T > C, p.(?). In the 2 patients with Lynch syndrome with colon adenocarcinoma (MSI-H), synchronous GISTs (1 patient quadruple WT and 1 patient kit ex 11 mutated ) were diagnosed; in the patient with ATM mutation, the diagnosis of GIST (kit ex 11 mutated) occurred after prostate adenocarcinoma and before colon adenocarcinoma (MSI-H). Conclusions: Our analysis suggests that GIST diagnosis could be tumor-related to multiple hereditary tumor syndromes as Lynch Syndrome and Ataxia-Teleangectasia syndrome, the latter being linked in eterozygosis to tumor susceptibility to breast in female. This report represents a high value in terms of genetic counseling for relatives and in terms of therapeutic implications for the patients.