For each patient, donor blocks of archived paraffin-embedded tissue were retrieved and two 1mm diameter cores were obtained from each sampling site: tumor center (TC), tumor periphery at invasive edge (TP), normal mucosa close/adjacent to tumor, normal mucosa well away from tumor, usually at the resection end margin, and from involved lymph nodes (LN). These were transferred into pre-drilled wells in a tissue microarray block and mounted on slides for immunohistochemistry.