Characterization of germline and somatic mutations in a Portuguese family with familial gastrointestinal stromal tumor

1. Characterization of germline and somatic mutations in a Portuguese family with familial gastrointestinal stromal tumor Isabel Veiga, M. Silva, J. Vieira, C. Pinto, M. Pinheiro, M. Soares, C. Coutinho, J. Dinis, N. Costa, P. Lopes, J. Guimarães dos Santos, C. Lopes, M. R. Teixeira Portuguese Institute of Oncology, Porto, Portugal

2. Characterization of germline and somatic mutations in a Portuguese family with familial GIST • Familial Gastrointestinal Stromal Tumor (GIST) is a rare autosomal dominant genetic disorder. • So far less than 20 of these families have been described. • Mainly with germline KIT mutations located at juxtamembrane domain (exon 11). Aims: Characterization of germline and somatic mutations in a Portuguese family with familial GIST.

3. I 12 Neo rectal? 78 1 2 3 4 Small bowel GIST 63y Gastric tumor? 68y 9 II 2 3 4 5 6 1 Rectal GIST 57y III 62 3 4 1 2 IV 25 29 Characterization of germline and somatic mutations in a Portuguese family with familial GIST Material • Proband • Rectal GIST – high risk (>10 mitoses/10 high power field) and a suspected stomach metastasis – intermediate risk (<1 mitose/10 high power field); • Partial response to Imatinib. • One aunt with multiple GIST in the small bowel – high risk (>10 mitoses/10 high power field); - Partial response to Imatinib. • The mother (obligate carrier) and the maternal grandfatherprobablydied of a gastric and a rectal neoplasia, respectively (without histological diagnosis available). 30 29

4. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Methods • Mutation screening of oncogenes KIT (exons 9, 11, 13 and 17) and PDGFRA (exons 12, 14 and 18) was performed by PCR and direct sequencing. • One tumor from the proband and another from the maternal aunt (with histologically confirmed GIST) were analyzed by Comparative Genomic Hybridization (CGH). • The suspected gastric metastasis was analysed by Fluorescent in Situ Hybridization (FISH).

5. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Results • A missense mutation was identified in exon 17 of KIT gene (D820Y) in the tumor and peripheral blood of the proband and in the tumor of the affected aunt. D820Y positive case Control case

6. I 12 Neo rectal? 78 1 2 3 4 Small bowel GIST 63y Gastric tumor? 68y 9 II 1 2 3 4 5 6 III Rectal GIST 57y 3 4 1 2 IV 25 29 Characterization of germline and somatic mutations in a Portuguese family with familial GIST Results • After informed consent, genetic testing was performed in 5 relatives at risk. • The D820Y mutation was identified in 3 assymptomatic relatives. + + 62 - - + + 30 29

7. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Results • CGH analysis of proband’srectalGIST. –14q –15q

8. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Results • FISH analysis of proband’ssuspected gastric metastasis did not find loss of 14q and 15q. +20q -22q • This genetic findings show that this lesion was not a metastasis of the rectal GIST, but an independent primary tumor.

9. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Results • CGH analysis of the small bowel GIST of the index’s aunt detected several losses and one gain, but none in common with the proband’s tumors. -1p21p32 -3q13q26 -9p21p24 -11 +12 -20q

10. Characterization of germline and somatic mutations in a Portuguese family with familial GIST Conclusions • This is the third family with the D820Ygermline mutationin KITexon 17 causing hereditarypredisposition to GIST. • Although both patients shared the same germline mutation (primary event), we demonstrate that the three GIST analyzed followed different pathogenetic pathways, each of which not significantly differentfrom what has been described in sporadic GIST. • To our knowledge this is the first study demonstrating different progressioncytogenetic pathways in familial GIST.