5568 Background: The response of tumor cells to platinum-based drugs involves DNA repair mechanisms. Platinum-DNA adducts are repaired by nucleotide excision repair (NER) enzymes that recognize the DNA damage and excise the platinum-DNA adducts from the injured DNA strand. Excision repair cross-complementation group 1 (ERCC1) is one of the genes that encode the proteins of the NER complex and several studies have linked ERCC1 to platinum resistance in cell lines and in human cancers. Cells with a high repair capacity, e.g. high level of ERCC1 expression may therefore be resistant to platinum-based chemotherapy, and conversely, polymorphisms within encoding DNA repair enzymes or low repair capacity may confer sensitivity. A common single nucleotide polymorphism (SNP) of ERCC1 at codon 118 have been proposed to impair ERCC1 translation and reduce ERCC1 protein expression and consequently influence the response to platinum based chemotherapy. The aim of this study was to evaluate ERCC1 expression and ERCC1 118 polymorphism in epithelial ovarian cancer and the potential association with response to platinum-based chemotherapy. Methods: Formalin-fixed, paraffin-embedded tissue sections from 159 patients with epithelial ovarian cancer, FIGO stage IIb-IV, were used for immunohistochemistry (monoclonal mouse antibody, clone 8F1, Neomarkers). ERCC1 codon 118 SNP genotyping was performed by real time PCR, Taqman SNP genotyping assay. Results: ERCC1 protein overexpression was found in 37.7 % of the tumors. The response rate (normalization of CA125 during platinum-based chemotherapy) was 63.6 % (35/55) in patients with ERCC1-negative tumors compared to only 35.6 % (16/45) in patients with ERCC1-positive tumors. (p = 0.0052, χ²). Furthermore increasing immunohistochemical score (H-score) was associated with poorer response to chemotherapy. (p = 0.0006, Spearman`s). The T/T genotype (44 %) showed better response to chemotherapy than C/C + C/T (15 % + 41 %) variants (p=0.042). Conclusions: Patients with ERCC1-negative tumors appear to have significantly better response to platinumbased chemotherapy compared to patients with ERCC1-positive tumors. In addition the TT genotype seems to be favorable towards better response to platinum-based chemotherapy. No significant financial relationships to disclose.