PCNA and neoplasm: In this study, we analyzed the immunolabeling of iron-related proteins (Transferrin Receptor 1, Transferrin Receptor 2, and Ferritin Heavy chain 1) and Proliferating Cell Nuclear Antigen (PCNA) in canine SCO tubules under different microenvironments: associated with seminomas, within Sertoli cell tumors, and isolated from tumor cells.