KANKER PAYUDARA FAMILIAL: PENELUSURAN GENA PREDISPOSISI TERWARIS DAN PERHITUNGAN RISIKO

Samuel Johny Haryono, dr.,Sp.B(K)Onk., Prof. dr. Sofia Mubarika Haryana, M. Med. Sc., Ph.D.,

2012 | Disertasi | S3 Kedokteran Umum

Pendahuluan Kanker payudara dengan riwayat keluarga dipengaruhi faktor genetik dan lingkungan. Sekitar 5-10% dari kasus kanker payudara disebabkan oleh mutasi gena predisposisi terwaris. Walaupun identifikasi mutasi BRCA1 dan BRCA2 pada pasien dan keluarganya marak dilakukan di seluruh dunia, peran mutasi BRCA dan gena predisposisi lain di populasi Indonesia belum ditelusuri. Terdapat beberapa pendekatan dalam penelusuran gena predisposisi. Dengan melakukan penelusuran dan dikembangkan suatu model baru penilaian risiko untuk memperhitungkan faktor risiko genetik dan non genetik pada populasi Indonesia akan memberikan kontribusi skrining dan pencegahan kanker payudara familial yang lebih komprehensif. Metode Penelitian 408 sampel terpilih dari 1246 kohort di Jakarta, Yogyakarta dan Bali diambil spesimen darah dan jaringan untuk pemeriksaan PCR dan sequencing gena BRCA1 dan BRCA2 and p53. Rancangan penelitian adalah hybrid nested design sesuai dengan epidemiologi genetik berbasis keluarga, dibuat pedigree dan dipilih 26 keluarga teseleksi untuk dilakukan wholeexome sequencing, 3 diantaranya dilakukan linkage analysis. Untuk melacak dissease susceptible marker dikembangkan metode GWAS (Genome Wide Association Study )dengan pemeriksaan marker-marker SNP memakai microarray dari 200 sampel. Model Bayessian – Mendel Model digunakan untuk penilaian probabilitas risiko genetik dan non genetik. Pengolahan statistik dengan program R pada studi hybrid cohort ini dilakukan dengan model cox proportional-hazard regression untuk mendapatkan risiko kumulatif sepanjang hidup. Validasi model baru perhitungan risiko dengan membandingkan kurva ROC terhadap model Gail, Claus dan BRCAPRO. Polimorfisme pada SNP p53 codon 72 genotipe terbanyak GC 56%, CG 20%, CC 95% dengan polimorfisme gen MDM2 SNP genotipe terbanyak TG 64% dan TT 36%. Linkage analysis mengarah pada dugaan adanya gena predisposisi terwaris pada kromosom 3 dan 4. GWAS menemukan SNP dengan asosiasi bermakna dengan OR tertinggi rs2419565, rs2942428, rs10925947, rs6722296, rs 17030023, rs 12997287 dan rs 17115674 pada masing-masing kelompok menurut riwayat keluarga. Model perhitungan baru (Samanda) dikembangkan dengan memperhitungkan faktor risiko genetik, non genetik. Kesimpulan Ditemukan beberapa mutasi gena poligenik BRCA dan non BRCA dan gena predisposisi lain pada kromosom 3 dan 4 serta pemetaan polimorfisme dan SNP sebagai marker dissease susceptibility. Hasil ini digunakan untuk pengembangan model risiko baru yang memperhitungkan faktor genetik dan non genetik. Model penilaian risiko Samanda perlu diupdate kekiniannya dan terbuka untuk direvisi sesuai dengan pengumpulan data penelitian yang berkesinambungan.

Introduction Breast cancer with positive family history is due to the interaction between genetic and environment factors. An estimated 5-10% of familial breast cancer is associated with mutations of susceptibility genes. While BRCA mutation identification is a common practice worldwide, no study has determined the role of BRCA and other susceptibility genes mutation in Indonesian population. A few methods exist for the identification of susceptibility genes. With the identification of Indonesian susceptibility genes and the new risk assessment model of Indonesian population can contribute the further further screening and cancer prevention method. Materials and Methods 408 blood and tissue samples were collected from 1246 cohort in Jakarta, Yogyakarta and Bali for PCR and DNA sequencing of BRCA1/2 and p53. Study design is hybrid nested design with the family base genetic epidemiology approach. Pedigrees were constructed and 26 selected familiy pedigree were performed for whole-exome sequencing, 3 of which underwent linkage analysis. Genome-wide association study with with microarray on 200 samples were performed to identify other susceptibility genes using SNP markers. Bayesian-Mendel model was used to calculate the probability of genetic and non genetic risks. Statistical analysis of R programmend the cox proportional-hazard regression were used for this hybrid cohort study useda to determine the cumulative life-time risk. The new risk calculation model was validated by comparing the ROC curve amongs the Gail, Claus and BRCAPRO models. Results We found 10 mutations in BRCA1 and BRCA2. There were 2 (BRCA2) nonsense mutation and 8 (1 BRCA1 and 7 BCRA2) missense mutation p.Ile2627Ser and p.Leu2688Pro, were registerd at BIC as novel mutation. Other mutation of p.Met1652Ile and p.Ile3412Val were considered as candidate gene and were identified mostly at BRCA2 exon 11 and 27. SNPs p53 codon 72 were found with the genotype GC 56%, CG 20%, CC 95% and the polymorphism of the gen MDM2 the SNPs with the genotype TG 64% and TT 36%. Linkage analysis suggested the presence of other susceptibility genes on chromosome 3 and 4. Though further research is needed, this result confirmed the polygenic inheritance model of familial breast cancer. A few disease susceptibility markers had also been identified. A new risk assessment model for Indonesian population incorporating these results were developed, called SAMANDA. The GWAS (Genome Wide Association Study) reveals SNPs that significantly associated with the maximum odd ratios rs2419565, rs2942428, rs10925947, rs6722296, rs 17030023, rs 12997287 and rs 17115674 respectively grouped according to the family history. A new model of risk calculation (Samanda) was developed to assess the genetic and non genetic risks. Conclusion Several polygenic mutations of BRCAs, non BRCAs and other subseptible genes on chromosome 3 and 4 were reported. Polymorphism and SNPs as disease susceptibility markers were mapped. A new model of risk assessment was developed to calculate the genetic and non genetic factors. This model (Samanda) will be updated and publicly opened for further studies.

Kata Kunci : kanker payudara familial