Fixed tumors and organs were embedded in paraffin and unstained slides were prepared for immunostaining or stained with H&E. IHC staining was performed as previously described (21 (link)). Primary antibodies included rabbit anti-Ki67 (1:400), rabbit anti-CD31 (1:100) (#9027; #77699, Cell Signaling Technology), rabbit anti-cleaved PARP (1:50) and rabbit anti-cleaved-caspase-3 (1:200), detected by a biotinylated horse anti-rabbit IgG antibody (BA-1100, Vector Laboratories Inc., Burlingame, CA) secondary antibody. Anti-human-specific mitochondria IHC staining (AbCAM, Cambridge, MA, cat# ab92824) was performed at a 1:1000 dilution to visualize metastases. All slides were developed with DAB Impact (Vector Labs, Burlingame, CA), counterstained in Gill’s hematoxylin (Vector Labs) and mounted with Cytoseal XYL mounting media. Tissue images were acquired with a Keyence BZ-X700 microscope. Quantification of metastatic burden was performed by digital scanning of whole stained slides using a Pannoramic FLASH III system (3D Histech), followed by manual counting of metastatic lesions present in the tissue section. Quantification of Ki67-, CD31-, cleaved-PARP- and cleaved-caspase-3-positive tumor cells was performed by calculating the area of positive cells in 4–5 representative fields per section using the Keyence Hybrid Cell Count module.