PCNA and cancer: However, most striking of all was our finding that malignant tumors, most of which were moderately differentiated hepatocellular carcinomas (HCCs) with solid or trabecular growth patterns that stained strongly for PCNA and phospho-Rps6Ser235/6 (panels f, g, and h of Fig 5D), developed in ~50% of ΔS6 livers by ~1 year of age (Fig 5E).