Differential Pattern of Methylation within Hormone Receptor Negative Breast Cancers
D Chitale, A Botrell, KM Chen, L Whiteley, L Neimier, Z Zhang, G Divine, U Raju, MJ Worsham. Henry Ford Hospital, Detroit, MI
Background: Like all cancers, breast cancer is considered to result in part from the accumulation of multiple genetic alterations leading to oncogene overexpression and tumor suppressor loss. The role of epigenetic tumor suppressor gene silencing by promoter methylation in many genes is increasingly recognized as an early event in carcinogenesis. Our aim was to explore pattern of promotor methylation in a set of tumor suppressor genes in hormone receptor negative breast cancers.
Design: From a cohort of 196 ER-PR- breast cancers from 2001 to 2005 (156 triple negative tumors (TNT) and 40 Her2+), 30 cases (22 TNT, 8 Her2+) were randomly selected for this pilot methylation project. Formalin fixed paraffin embedded tumor DNA was interrogated for 24 tumor suppressor genes using the high throughput Methylation-Specific Multiplex Ligation Dependent Probe Amplification (MS-MLPA). All H & E slides were reviewed and the tumors were classified into medullary, atypical medullary (AMC) and non-medullary (NMC)subtypes and results compared with the methylation data.
Results: Promotor methylation was noted in 21/24 genes: TIMP3, APC, CDKN2A, MLH1, RARB, CDKN2B, HIC1, BRCA1, CASP8, PTEN, BRCA2, CD44, RASSF1, DAPK1, VHL, ESR1, TP73, FHIT, IGSF4, CDH13, GSTP1. The most frequently methylated genes were MLH1-16/30 (53.3%), RASSF1-15/30 (50%), CDH13-12/18 (40%), CDKN2B,GSTP1-9/30 (30%), CDKN2A (26.7%), BRCA1, BRCA2,RARB-6/30 (20%). CDKN1B, ATM, and CHFR genes were unmethylated in this group. RASSF1 was significantly methylated among the Her2+ group-7/8 (88%) compared to the TNT-8/22 (36%) (p=0.035). In contrast, BRCA1,BRCA2-6/22 (37.5%) were frequently methylated in the TNT subgroup (trend, p= 0.155). Only one case of methylated BRCA1 was co-methylated with BRCA2, others being mutually exclusive. All the 8 Her2+ cases had unmethylated BRCA1/2. There were 8/30 AMC (all TNT) and 22 NMC (8/22 Her2+). No correlation was observed between histology and methylation patterns.
Conclusions: Breast cancer is a heterogeneous disease with different outcomes, TNT's having an adverse prognosis. The emerging differential methylation pattern within hormone receptor negative breast cancers would further help stratify them into distinct subgroups. Promotor methylation being potentially reversible, methylated genes may serve as future molecular targets for demethylating therapies. Support: NIH R01 DE15990.
Monday, March 9, 2009 1:00 PM
Poster Session II # 43, Monday Afternoon