Caracterização molecular dos tumores desmóides / Molecular characterization of desmoid tumors

Os tumores desmóides são proliferações mesenquimais fibroblásticas que, apesar de não originarem metástase, são extremamente invasivos localmente. Esses tumores podem ser esporádicos ou relacionados a síndromes genéticas, como a polipose adenomatosa familiar (FAP). Algumas alterações moleculares já foram relatadas, entretanto, a tumorigênese desses tumores ainda não é totalmente compreendida. Assim, o objetivo desse estudo é analisar e comparar o espectro de mutações somáticas nos tumores desmóides esporádicos e associados a síndromes. Dez tumores desmóides foram analisados por sequenciamento do exoma. O DNA extraído foi utilizado para a construção de uma biblioteca. O DNA fragmentado foi hibridizado com moléculas de RNA correspondentes à região do exoma (50Mb) e posteriormente capturado. As bibliotecas foram amplificadas através de PCR em emulsão e sequenciadas utilizando o SOLiD™ 4 System. Os dados de sequenciamento foram analisados através de programas específicos, e as variantes identificadas somente no tecido tumoral foram selecionadas. A validação de algumas variantes foi realizada por sequenciamento alvo (target sequencing), por ser um método mais sensível através do Ion AmpliSeq e sequenciamento na plataforma Ion PGM.

Desmoid tumors (DTs) are unique mesenchymal fibroblastic proliferationsthat, despite the absolute lack of ability to metastasize, are extremely locallyinvasive. The great majority of DTs occur sporadically, most of these arecaused by somatic mutations in β-catenin (CTNNB1) that lead to aconstitutive activation of WNT pathway. A small number of DTs can occur inthe background of familial adenomatous polyposis (FAP) and are associatedwith inactivating germline mutations in the adenomatous polyposis coli (APC)gene. However, as the genetic profile of desmoid tumors has not beenstudied extensively and remains poorly characterized, the aim of this projectwas to analyze the spectrum of somatic mutations in desmoid tumors. TenDTs were analyzed by massive parallel sequencing (exome). DNA wascaptured by hybridization in solution to cRNA oligonucleotide baits, subjectedto an emulsion PCR, and then sequenced using the SOLiD™ 4 System. Thesequence data were analyzed through specific bioinformatics software andthe variants identified only in tumor were selected for further validation. Forthe sake of higher sensitivity and specificity, target sequencing usingcustomized Ion AmpliSeq™ panels on the Ion PGM™ plataform were used tovalidate the alterations observed using the SOLiD™ 4.

Involvement of signaling molecules in the prediction of response to imatinib treatment in metastatic GIST patients.

Imatinib therapy has undoubtedly contributed to the treatment of metastatic gastrointestinal stromal (GIST) tumors that were previously untreatable. However, disease progression during treatment with tyrosine kinase inhibitors remains an issue in clinical practice not fully explained by KIT and PDGFRA mutation status. We investigated the role of three important signaling molecules (insulin-like growth factor 1 receptor [IGF1R], protein kinase C-θ [PKCθ], and Raf kinase inhibitor protein [RKIP]) that have been implicated in GIST pathogenesis as potential biomarkers for prediction of response to imatinib treatment. We retrospectively reviewed 76 patients with metastatic GIST submitted to imatinib treatment between 2002 and 2007, and analyzed 63 of them. Insulin-like growth factor 1, total PKCθ, phosphorylated PKCθ, and RKIP immunohistochemical expression were correlated with objective response to imatinib treatment and progression-free and overall survival. Median follow-up was 31.2 mo (95% confidence interval, 26.3-36.1 mo). There was a statistically significant association between IGF1R expression and type of response to imatinib treatment (P = 0.05)-that is, higher IGF1R expression was related to lower objective response. However, IGF1R higher expression did not affect progression-free and overall survival. Insulin-like growth factor 1, but not PKCθ and RKIP, emerges as a potential biomarker for prediction of response to imatinib treatment in metastatic GISTs. Validation studies are warranted.

Prognostic relevance of KIT and PDGFRA mutations in gastrointestinal stromal tumors.

BACKGROUND: Prediction of biological behavior is crucial for selection of new therapeutic modalities in GIST. Here, we aimed to assess whether KIT and PDGFRA mutations have survival impact in gastrointestinal stromal tumors (GIST). PATIENTS AND METHODS: Fifty-five Brazilian patients with completely resected GIST were examined for KIT and PDGFRA mutations. The 5-year disease-free survival (DFS) was analyzed. RESULTS: KIT and PDGFRA mutations were identified in 74.5% and 7.3% of patients, respectively. The 5-year DFS rate for all patients was 52.8%. The 5-year DFS rate was lower in patients with tumors having in-frame deletions or concomitant in-frame deletions and insertions affecting codons 557-558 than in patients with tumors having other exon 11 KIT mutations (p=0.023). Conversely, when the patients with concomitant deletion-insertion mutations affecting codons 557-558 were excluded from the analysis, deletions involving codons 557-558 had no influence on 5-year DFS rates. CONCLUSION: Our findings indicate that a specific KIT mutation may be associated with unfavorable behavior in GIST. This finding may have implications on selecting patients for adjuvant therapy.