PTK7 protein expression

Tumor-associated PTK7 protein expression levels were assessed by a Clinical Laboratory Improvement Amendments–validated IHC assay in formalin-fixed, paraffin-embedded tumor tissue samples collected from patients, as described previously (15). Digital tissue analysis was performed using the Flagship Biosciences proprietary Image Analysis platform. At least 90% of cells quantified by the algorithm were tumor cells. H-scores were determined from image analysis mark-up (regions of analysis) and quantified on the basis of percentage of positive cells and staining intensity. If a sample failed digital tissue analysis, a visual assessment was performed for nonquantitative plasma membrane staining. All analytic markups were reviewed and accepted by a board-certified MD pathologist. H-scores were rank ordered lowest to highest and divided into tertiles. Tumor H-scores were divided into relatively low, moderate, and high PTK7 expression categories based on tertiles.