Development and Validation of an ERCC1 Immunohistochemistry Assay for Solid Tumors

Context.- Excision repair cross-complementation 1 (ERCC1) is a key enzyme in nuclear excision repair pathway and has a critical role in helping remove DNA adducts caused by cross-linking agents, such as platinum-containing cancer chemotherapies and other DNA-damaging therapeutic modalities. ERCC1 expression, evaluated by techniques such as immunohistochemistry, has been associated with clinical response; ERCC1+ tumors are more resistant to cisplatin treatment than are ERCC1(-) tumors. Although several immunohistochemistry, anti-ERCC1 antibodies are available, the 8F1 clone, in particular, has been used in many studies. Recent evidence has suggested that the 8F1 antibody cross-reacts with at least one other protein, raising concerns about the specificity of this clone. Objective.- To design an immunohistochemistry assay to detect ERCC1 levels that show dynamic range and consistent analytic performance. Design.- Two different primary antibodies to ERCC1,clones 4F9 and D6G6, were evaluated on formalin-fixed, paraffin-embedded tissue. We then performed a fit-forpurpose assay validation with the 4F9 clone, which included sensitivity assessment across several solid tumor types and evaluation of analytic parameters, such as precision and reproducibility. Results.- The 4F9 clone was consistently superior to the D6G6 clone in the optimization phase. A range of expression was seen in ovarian, head and neck, non-small cell lung, and esophageal cancer samples when tested with the 4F9 clone. The antibody showed acceptable reproducibility (31.02%) and precision (16.06%). Conclusions.- This assay can be used to assess ERCC1 levels during clinical studies of patient tumors from a variety of tumor types.