This process is performed in Oncology Tissue Services Core of Johns Hopkins University School of Medicine. Immunolabeling for p21, p16 and γH2AX is performed on formalin‐fixed, paraffin embedded sections (5 μm) on a Ventana Discovery Ultra autostainer. Following dewaxing and rehydration on board, epitope retrieval is performed using Ventana Ultra CC1 buffer at 96oC for 64 minutes. Primary antibody is applied at 36oC for 60 minutes. Primary antibodies are detected using an anti-rabbit HQ detection system followed by Chromomap DAB IHC detection kit, counterstaining with Mayer’s hematoxylin, dehydration and mounting.