13-gene signature to predict rapid development of brain metastases in patients with HER2-positive advanced breast cancer.

Abstract

505 Background: Brain metastases (BM) of breast cancer constitute an important part of therapeutic failures and are associated with severe morbidity and mortality. The risk of BM is particularly high in HER2+ advanced breast cancer pts. We earlier developed in this group a 13-gene signature strongly predicting for rapid development of BM (J Clin Oncol 2008; 26: 45s). Now, we validated these results in an independent group of pts and on culture model system. Methods: Discovery group included 87 samples analyzed using cDNA synthesis, annealing, selection, extension, ligation and array hybridization (DASL). Independent validation group included 75 samples analyzed using quantitative reverse-transcriptase PCR. 3D culture validation model system used immortal, non-tumorigenic human MCF10A breast epithelial cells with and without ectopic expression of HER-2 and RAD51, a DNA double strand break repair gene (one of the three genes of this group overexpressed in 13-gene signature). The number and morphology of breast acini were scored using indirect immunoflourescence and confocal microscopy. Results: Median brain metastasis-free survival (BMFS) in the discovery group for ‘high’ vs. ‘low’ expression signature tumors was 36 months and 66 months, respectively (P=0.0068), and in the validation group 54 and 86 months, respectively (P=0.032). Short BMFS was also associated with ER-negativity; BMFS in the cohort of ‘high’ 13-gene signature and ER- tumors vs. other 3 groups was 31 months and 66 months in discovery group, and 41 and 77 months in validation group (P<0.0001 and P=0.02, respectively). Overexpression of RAD51 in MCF-10A breast cells altered their three-dimensional acinar morphology and increased the percentage of invasive structures by 6.5 fold, both in the presence and absence of HER2 overexpression. Conclusions: 13-gene signature and ER-negativity predict rapid development of BM in HER+ advanced breast cancer pts. RAD51 may promote aggressiveness in breast epithelial cells. These data may be useful in the design of BM preventive trials and may prompt new treatment strategies.