Drosha and Dicer Down-Regulation in Breast Cancer: A QRT-PCR Analysis
R Natrajan, F Geyer, MB Lambros, MA Lopez-Garcia, K Savage, JS Reis-Filho. Institute of Cancer Research, London, United Kingdom; Hospital Universitario Virgen del Rocio, Seville, Spain
Background: Non-coding RNAs, in particular miRNAs, play major roles in the development of cancer and global down-regulation of miRNAs has been documented in human cancers. Drosha and Dicer are two key enzymes in the miRNA machinery, whose down-regulation was described in ovarian cancers of aggressive clinical behaviour. Here we investigated the prevalence of Drosha and Dicer down-regulation in breast cancers and their associations with clinicopathological features of the tumours and patients' outcome.
Design: A cohort of 245 patients with invasive breast cancer treated with therapeutic surgery followed by adjuvant anthracycline-based chemotherapy and a series of ten normal breast samples from reduction mammoplasties were retrieved from the histopathology files of the authors' institutions. mRNA was extracted from representative sections of the tumours containing >50% of tumour cells and from sections of normal breast samples enriched for terminal duct-lobular units (>50% of the surface area). TaqMan quantitative real-time PCR (qRT-PCR) using primers for Drosha and Dicer and for two house keeping genes was performed. Cases were categorised as displaying Drosha or Dicer down-regulation if expression levels were lower than the median expression levels in normal breast tissue and correlated with clinicopathological characteristics of the tumours and patients outcome.
Results: Drosha down-regulation was observed in 18% of cases and was significantly associated with histological grade, high MIB1 labelling index, HER2 expression and gene amplification, TOP2A gene amplification and inversely correlated with BCL2 expression. Dicer down-regulation was found in 46% cases and was significantly associated with histological grade, presence of lympho-vascular invasion, basal markers (EGFR, cytokeratins 5/6 and 17, caveolin 1 and nestin), high MIB1 labelling index and triple negative phenotype and inversely correlated with oestrogen receptor and BCL2 expression. Drosha down-regulation was significantly more prevalent in HER2 positive cancers, whereas the majority of basal-like (76%) and triple negative (78%) cancers displayed Dicer down-regulation. No associations between down-regulation of Drosha and Dicer and outcome were observed.
Conclusions: Drosha and Dicer are preferentially down-regulated in HER2 and basal-like cancers, respectively. Distinct components of the miRNA machinery may be dysfunctional in different subtypes of breast cancer.
Monday, March 22, 2010 1:00 PM
Poster Session II # 63, Monday Afternoon