MKI67 and testicular germ cell tumor: The Ki-67 labeling index, a well-validated biomarker of cell proliferation, correlates positively with tumor proliferative capacity and inversely with histological differentiation grade.[14,15] In our patient with IAD and testicular germ cell tumor, immunohistochemistry (Fig. 2) showed a Ki-67 index of 20%, positive staining for SALL4 and PLAP (confirming poorly differentiated intratubular germ cell neoplasia in situ), and negative ACTH staining (ruling out ectopic ACTH expression).