BACKGROUND: Platinum-based chemotherapy is part of the standard treatment for patients with colorectal cancer. ERCC1 is a potential predictive biomarker for platinum-based chemotherapy. The aim of this study was to examine interobserver agreement on ERCC1 protein expression in primary colorectal cancer as well as corresponding liver metastasis. Furthermore, comparison of ERCC1-expression in primary tumor and the corresponding liver metastasis was performed.

METHODS: Forty patients with primary colorectal cancers and corresponding liver metastases were included. One slide was stained with the anti-ERCC1 antibody, 4F9 clone (DAKO) and evaluated by two gastrointestinal pathology consultants and a pathology registrar separately. Interobserver agreement was evaluated for primary tumors and liver metastases using kappa (κ) statistics. Discordant scorings were reviewed, and consensus was obtained. The expression in primary tumor was compared with the corresponding liver metastases.

RESULTS: For the primary tumors agreement was found in 85% of the tumors corresponding to an unweighted kappa value of 0,79 (95% CI 0,64-0,94). For the liver metastases agreement was found in 76% corresponding to an unweighted kappa value of 0,64 (95% CI 0,49-0,79). When comparing primary tumors to the corresponding metastases, no concordance in ERCC1-expression was observed.

CONCLUSION: Interobserver agreement of ERCC1 expression was good for both primary tumors and liver metastases, which is crucial for a potential predictive biomarker. As no concordance between primary tumor and liver metastases was found it seems to be of high importance to use tissue from actual tumor burden for evaluation of ERCC1 expression. Further studies and correlation to clinical outcome are warranted.