PTEN Loss of Expression Is Not Related with PTEN Promoter Hypermethylation in HER2-Positive Breast Carcinoma
D Giner, L Sanchez-Tejada, FJ Gutierrez-Avino, L Perez-Carbonell, FI Aranda, E Lerma, L Catasus, G Peiro. Hospital General Universitari, Alacant, Spain; Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
Background: PTEN expression is reduced in at least 50% of breast carcinomas (BC) in the absence of mutations. This underexpression can be related to epigenetic factors, such as gene promoter hypermethylation, which has been reported in several human neoplasms. The aim of our study was to analyze the expression of PTEN by immunohistochemistry (IHC) and PTEN methylation status by Methylated Specific PCR (MSP) analysis after discrimination of the pseudogene psiPTEN, in a series of HER2-positive BC.
Design: We evaluated in 210 HER2-positive (3+ in >30% cells by IHC or amplification by FISH/CISH) BC the PTEN expression (Dako) by IHC. DNA methylation patterns in the PTEN promoter were determined by MSP in 68 BC (34 PTEN-positive and 34 with PTEN loss). Briefly, 1 μg of genomic DNA from tumor samples was subjected to bisulfite modification (Epitec Bisulfite Kit; Qiagen). PCR was carried out using specific primers (methylated or unmethylated). Commercial genomic DNA was used as negative and positive controls, after treatment with CpG methyltransferase M.SssI (New England BioLabs). PCR products were analyzed using 2100 Bioanalyzer. The results were correlated with clinical-pathological parameters and the outcome.
Results: Patients' average age was 58 years (range 24-87 years) with a median follow-up of 73 months. Tumors were more frequently of high grade (94.8 %), with necrosis (51%) and lymphatic invasion (54.8 %). PTEN loss of expression (complete absence) was seen in 16.2% (34/210) tumors. PTEN was predominantly preserved in tumors of younger patients (p=0.003), with <2 cm in size (p=0.004), and a trend with lower grade (p=0.10), but without differences for presence of necrosis, vascular invasion or lymph-node status (p=ns). The molecular analysis revealed 98.3% samples without promoter hypermethylation, and only 1 tumor PTEN-positive showing partial methylation (1.7%). Patients with PTEN-positive tumors had better disease-free survival than those with PTEN loss (66.4% vs 50%; p=0.048), but the overall survival was not different (76% versus 69%; p=ns) (Kaplan-Meier; log rang test).
Conclusions: In our series of HER2-positive BC, 16.2% showed PTEN loss. The lack of association between absence of PTEN and promoter hypermethylation status suggests that in addition to mutations, another epigenetic factors such as protein degradation, may contribute to this alteration in this subtype of BC. Supported by grant FIS 06/1495.
Monday, March 22, 2010 1:00 PM
Poster Session II # 57, Monday Afternoon