Immunohistochemical status of epidermal growth factor receptor (EGFR) in primary colorectal carcinoma and their related metastases

Abstract

3711 Background: Treatment using monoclonal antibody targeting EGFR (Erbitux) has been recently approved in advanced colorectal cancer (CRC). It requires an immunohistochemical (IHC) assessment for patient eligibility. Controversial and limited data are available on the EGFR status in distant metastases. Because of clinical implications, we studied EGFR expression on primary CRC and their related metastases, to assess wether EGFR IHC status was similar on both sites. Methods: EGFR immunohistochemistry was evaluated from primary tumors and related synchronous metastatic sites in 32 CRC patients. The primary tumor was situated in the colon for 21 patients and in the rectum for 11 patients. The analyzed metastatic sites were the liver (n = 31) and the ovary (n = 1). An IHC standardized assay was used (EGFR pharm Dx, DakoCytomation) on paraffin embedded sections. EGFR positive status (EGFR +) was defined by a percentage of tumoral stained cells ≥1%, displaying a membranous pattern. For primary CRC, EGFR assessment was performed on tissue sections with the deepest tumoral areas, known to contain the strongest immunoreactivity. Results: 84% of the CRC cases (27/32) and 91% of the metastases (30/32) were EGFR +. Twenty five out of 27 EGFR + primary cases (93%) showed a metastatic positive status. Moreover, the number of EGFR + tumoral cells in the primary site was significantly correlated with those observed in the metastases (r2= 0.616, p= 0.0002). Two EGFR + primary sites had a negative metastatic EGFR expression and 5 EGFR + metastatic sites had a negative primary site expression. However, these discordant cases were not statistically significant (p= 0.453). Conclusions: Despite the limited number of cases, our results suggest that EGFR expression is frequent and similar on both primary and metastatic sites. These data may be of clinical interest because i) treatment decision is based on EGFR immunoreactivity and ii) tumoral material of both sites is not always concomitantly available. In order to precisely define a practical approach, assessment of EGFR expression on additional series, containing synchronous and metachronous metastatic sites of different origin, needs to be performed. No significant financial relationships to disclose.