ERBB2 and colorectal adenocarcinoma: The in vitro combination effect of HER2-TTC and PARPi olaparib was evaluated on the colorectal adenocarcinoma cell line DLD-1 parental and DLD-1 BRCA2 -/- Firstly, we determined the expression of HER2 antigens on the surface of the cell lines by flow cytometry.