Somatic mutation and polymorphism analysis in pleomorphic adenomas of the salivary glands

Abstract

Background: Genetic studies of salivary gland neoplasms were mainly focused on chromosomal changes, and some specific patterns of chromosome translocations have been described. However, molecular alterations, in particular the role of HER-2/H-ras/c-myc signalling cascade in pleomorphic adenoma pathogenesis (PA), are less well characterized. In addition, data on single nucleotide polymorphisms (SNPs) as potential susceptibility factors for PA development are also quite scarce. Methods: Mutational analyses were performed by means of real-time PCR (HER-2 and c-myc amplification analysis), PCR-SSCP and sequencing (H-ras point mutation detection). Polymorphisms analysis was performed by PCR-RFLP (survivin and MMP-9 genes). Results: Amplification of HER-2 and c-myc has been found in 13% and 9% of PA cases respectively. Point mutations in H-ras codons 12/13 have been detected in 17% of PAs. No correlation could be established between these alterations and clinical characteristics of PAs, whereas they might play a role in a subset of malignant salivary gland tumours. As for survivin -31 G/C polymorphism, C allele carriers had a 4-fold decrease of the risk of developing PA (p=0.05). Carriers of the variant allele T of the -1562C/T SNP in MMP-9 gene had a 4-fold increase of the risk of developing PA (p lt 0.001). Conclusions: A longer follow-up of PA patients harbouring mutations could uncover a prognostic role of HER-2 and c-myc amplification as predictors of adenoma transformation into carcinoma. Both survivin and MMP-9 promoter polymorphisms represent susceptibility factors for the development of PAs in the Serbian population.

Uvod: U ispitivanjima mehanizama nastanka tumora pljuvačnih žlezda uglavnom dominiraju citogenetičke studije, pa su tako detektovane i opisane različite hromozomske translokacije sa specifičnim obrascem javljanja. Međutim, molekularne promene u ovim tumorima i dalje su relativno slabo poznate, a pogotovo je malo podataka o potencijalnom značaju signalnog puta HER-2/H-ras/c-myc u razvoju i progresiji pleomorfnih adenoma (PA). Takođe, retki su i podaci 0 polimorfizmima pojedinačnog nukleotida (SNP) kao faktora predispozicije za nastanak PA. Metode: Analize somatskih mutacija urađene su metodama real-time PCR (analiza amplifikacije HER-2 i c-myc), PCR-SSCP i sekvenciranja (detekcija tačkastih mutacija u H-ras). Ana I iza polimorfizama pojedinačnih nukleotida (SNP) vršena je prime- nom metode PCR-RFLP (u genima za survivin i MMP-9). Rezultati: Amplifikacija gena HER-2 detektovana je u 13%, c-myc u 9% a tačkaste mutacije u kodonima 12/13 H-ras gena u 17% uzoraka. Nije ustanovljena veza između ovih promena i kliničkih odlika adenoma. Na malom uzorku karcinoma, pokazano je da je amplifikacija HER-2 povezana sa recidivima tumora. Nosioci C alela u -31G/C SNP gena za survivin imaju četiri puta manji rizik od nastanka PA (p=0,05), dok nosioci varijantnog alela T kod -1562 C/T SNP u MMP-9 genu imaju četiri puta veći rizik da obole od PA u odnosu na kontrolu (p lt 0,001). Zaključak: Dužim praćenjem pacijenata sa PA mogla bi da se ustanovi prognostička uloga HER-2 i c-myc amplifikacija kao indikatora za transformaciju adenoma u karcinom. Polimorfizmi u promotorima gena za survivin i MMP-9 predstavljaju modulatore rizika za razvoj pleomorfnih adenoma u srpskoj populaciji.