#6050 Background: Breast cancer cells lacking the DNA repair mechanism Homologous Recombination (HR) have recently been shown to be hypersensitive to bifunctional alkylating agents such as carboplatin and poly(ADP-ribose)polymerase(PARP)-inhibitors, a novel class of targeted agents. We have previously reported the construction of an array Comparative Genomic Hybridization (aCGH) classifier that detects the characteristic copy number aberrations of BRCA1-mutated tumors which are thought to be caused by HR deficiency. We hypothesized that metastatic breast cancer patients with tumors harboring such a BRCA1-profile may specifically benefit (longer progression-free survival (PFS)) from intensive treatment with bifunctional alkylating agents compared to patients without this tumor-profile.
 Methods: We isolated DNA from formalin-fixed paraffin-embedded primary tumor tissue collected from 3 prior studies carried out in our institute, in which metastatic breast cancer patients received intensive alkylating chemotherapy with carboplatin, thiotepa and cyclophosphamide (CTC). DNA from 40 tumors was tested for the presence of the BRCA1-profile by aCGH. Furthermore, we screened for the majority of BRCA1 and BRCA2 mutations that frequently occur in Dutch BRCA1 and BRCA2 families.
 Results: Sixteen patients had a tumor with a BRCA1-profile and had a better response to CTC-treatment, defined by achievement of a complete remission (p=0.01) and longer PFS (p=0.001, figure 1), with a hazard ratio for progression of 0.30 (p=0.002).
 
 All 6 patients who remain in continuous complete remission (56+ to 150+ months) had a tumor with a BRCA1 profile. Two BRCA1 and 2 BRCA2 mutations were found in 4 patients of whom 3 had a BRCA1-profile and a long PFS (> 30months), linking HR deficiency (BRCA1 and BRCA2 mutations) in breast cancer patients to good outcome on platinum-based chemotherapy.
 Discussion: Using an aCGH classifier initially constructed to identify BRCA1-mutated tumors we were able to identify a group of metastatic breast cancer patients treated with platinum-based chemotherapy with a high complete remission-rate and long progression free survival. Moreover, this group contained all patients who were apparently cured by intensive alkylating chemotherapy. Our aCGH assay may represent an effective test for BRCA-ness and could be important to select patients with sporadic tumors for therapy targeted at cells deficient in Homologous Recombination. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6050.

Background: Breast cancer cells deficient for BRCA1 are hypersensitive to agents eventually resulting in double-strand DNA breaks, such as platinating agents and poly(ADP-ribose)polymerase (PARP)-inhibitors. Using a BRCA1 array comparative genomic hybridization (aCGH) classifier, we previously identified BRCA1-like tumors with a functional BRCA1-loss, caused by BRCA1-mutation, BRCA1-promoter methylation, or an as yet unidentified mechanism. We observed that these BRCA1- like(CGH) tumors showed an expansive growth pattern, one of the histological features of BRCA1-mutated breast cancer. The aim of this study was to determine which combination of histological features associated with BRCA1-mutated breast cancer were present in the BRCA1-like(CGH) subtype and might predict sensitivity to platinating chemotherapy. Methods: We studied histological features, which are known to be associated with BRCA1-mutations in literature: growth pattern, necrosis, lymphocytic infiltrate and mitotic count. In an independent series of metastatic breast cancer patients (MBC, n=39) for which BRCA1- like(CGH) status was known, whole slides were scored for all features. Features were first tested for significant association with BRCA1- like(CGH) status. Next, significantly associated features were tried in different combinations to find the highest sensitivity to predict for BRCA1- like(CGH) status (BRCA1-histological combination). This histological combination was subsequently tested in stage-III estrogen-receptor low, HER2-negative breast cancer patients, who had been randomized between adjuvant high-dose (HD) platinum-based alkylating chemotherapy and conventional chemotherapy. Additionally, we assessed the association of BRCA1-like(aCGH) status and BRCA1-loss through mutation or promoter methylation with the histological combination in a random subgroup. Results: The combination of a ‘mitotic count above 19 per 2 mm2 with either ‘an expansive growth pattern’ or ‘necrosis’ correctly identified the BRCA1-like(CGH) tumors with a sensitivity of 88% and a specificity of 86% in the MBC patients. In the adjuvant stage-III series, greater benefit was observed from HD-platinum-based chemotherapy versus conventional chemotherapy among patients with the BRCA1-histological combination (41/136=30%, multivariate HR=0.20, 95%CI 0.07-0.62; 7-year recurrence free survival (RFS) 78% versus 39%), compared to patients with other histological features (95/136=70%, HR=0.53, 95%CI 0.29-0.95, 7-year RFS 55% versus 43%), although without a significant difference (test for interaction p=0.14). Analyses of patients with tumors with a mitotic count above 19 only, showed similar results for the BRCA1-histological combination (in this subgroup: expansive growth or necrosis, p-interaction: 0.07). The BRCA1-histological combination was significantly associated with BRCA1-like(CGH) status and BRCA1-mutations, but not with BRCA1-promoter methylation. Conclusion: Using histology only, we were able to identify a large proportion of the aCGH defined BRCA1 molecular subtype. Here, we present the first data that histology might be a biomarker for identifying high-risk patients benefiting from platinum-based chemotherapy in the absence of molecular-based techniques. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD01-04.