Background: Approximately 20-25% of ovarian cancers are attributable to germline or somatic BRCA1/2 mutations, resulting in defects in the homologous recombination pathway. Inactivation of these genes can also be mediated by epigenetic changes, e.g., hypermethylation of CpG islands in the promoter regions. In such homologous recombination deficient tumors, platinum based chemotherapy is in general effective, however, loss of hypermethylation might lead to refractory disease. The aim of this study was to evaluate the stability of BRCA1 promoter hypermethylation in recurrent disease after platinum based chemotherapy.Methods: Tumor tissue from 76 patients with primary and 48 patients with platinum-sensitive recurrent high-grade ovarian cancer was collected. In a subgroup of 12 patients, 'paired' tumor tissue from primary and recurrent surgery was available. BRCA1 promoter methylation status was assessed using methylation specific polymerase chain reaction and was verified by Sanger Sequencing.Results: 73.7% (56/76) of primary and 20.8% (10/48) of recurrent tumors displayed BRCA1 promoter hypermethylation. BRCA1 promoter methylation status was not associated with progression-free-or overall survival. In the paired subgroup 83.3% (10/12) of the primary vs. 16.7% (2/12) of the recurrent tumors showed hypermethylation. In eight patients loss of BRCA1 hypermethylation was observed, whereas two patients had stable methylation status.Conclusions: Loss of BRCA1 promoter methylation may be a mechanism to restore BRCA1 function in recurrent disease. However, currently the clinical significance is still unclear and should be evaluated in prospective clinical trials.

#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.

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