Use of HER2 gene amplification to identify patients with metastatic colorectal cancer resistant to anti-EGFR monoclonal antibodies.

Abstract

474 Background: KRAS mutation represents the only validated biomarker used in clinical practice for selection of metastatic colorectal cancer (mCRC) candidates for therapy with the anti-Epidermal Growth Factor Receptor (EGFR) monoclonal antibodies. Previous studies conducted in small cohorts of patients suggested that HER2, the major EGFR partner, could modify the sensitivity to anti-EGFR agents. Aim of the present study was to investigate the role of HER2 gene status in a cohort of mCRC patients treated with cetuximab or panitumumab. Methods: 266 chemorefractory mCRC patients treated with cetuximab or panitumumab alone or in combination with chemotherapy were collected in an international consortium effort. HER2 gene status was analyzed using the dual-color FISH assay LSI HER2/neu-CEP17 (PATHVYSION, Abbott) in one central lab, whereas KRAS/BRAF mutations were investigated locally. HER2 gene amplification was defined as the presence of a ratio between HER2 gene and chromosome 17 centromere > 2. Results: An objective response to anti-EGFR therapy (complete or partial response according to RECIST criteria) was observed in 79/266 (29%) of patients. Twelve cases (4.5%) showed the classical pattern of HER2 gene amplification (R>2) in the whole tissue (>80% of tumor cells). By matching HER2 gene status with clinical response we observed that HER2 gene amplification was significantly related to therapy resistance (p<0.0001). Moreover, analysis of follow-up data indicated that HER2 gene amplification was significantly associated with a worse progression free survival (PFS, p=0.0025) and with a trend for a worse overall survival (p=0.062). Similar associations were also observed in the KRAS/BRAF wild-type patients. Conclusions: Data from this large retrospective study suggest that HER2 gene status evaluated by FISH may represent an additional marker useful for the prediction of mCRC patients’ response to EGFR-targeted therapies, in line with very recent evidence. In particular, patients with HER2 gene amplification seem to be resistant and show a shorter PFS. Future studies are needed to deeply investigate the clinical and biological meaning of HER2 gene status deregulation in mCRC.