RB1 and neoplasm: Tumor sections of UPEN‐RB‐175 (MYCN‐amplified, RB1+/+) stained strongly for pRb and ppRb (Fig. 4B,D), while the two MYCN‐amplified RB1+/− stained strongly with pRb antibody (Fig. 4F,J), but showed weaker staining of fewer cells with ppRb antibody (Fig. 4H,L).