Verdu Ma, b, Trias Ia,b,c, Roman Rb, Rodon Nb, Pubill Ca, Puig Xa,b,c
a Histopat Laboratoris, Barcelona, Spain. b BIOPAT, Biopatologia Molecular, Grup Assistencia, Barcelona, Spain. c Hospital de Barcelona, SCIAS, Grup Assistencia, Barcelona, Spain
Recently, the study of the EGFR mutations in lung cancer has become mandatory due to their usefulness in target therapy. Lately, the use of specific antibodies to study themost prevalent of these mutations has been introduced. The newly published discovery of the existence of a cross-reaction between the HER2 protein and the EGFR L858R-specific antibody in breast cancer led us to corroborate this cross-reactivity in other tumors; specifically, we have chosen gastric carcinomas where HER2 is routinely evaluated as a molecular therapy driver. Our series consists of 15 primary gastric carcinomas, 7 HER2 cases positive for overexpression/amplification and 8 negative cases for both techniques. EGFR L858R mutation was studied with immunohistochemistry and complemented with real time PCR when positive. Immunohistochemistry assay with EGFR L858R was positive in 5 of the HER2 positive carcinomas (71%), none of which was confirmed by PCR, and negative in all HER2 negative carcinomas.
The EGFR L858R antibody gives false positive results in most gastric carcinomas with HER2 overexpression/amplification, confirming the results described previously in breast cancer. It is also important to bear in mind that HER2 has also been described in other carcinomas, including lung cancer.