RESUMO
Renal tumours were induced in female mice 132 days after intravenous administration of streptozotocin. The tumours exhibited papillary and/or solid architecture with papillary tumours showing no histological evidence of malignancy. Malignant behaviour, manifest as infiltration of adjacent renal tissue and lymphatic infiltration, was noted for tumours with solid architecture. Intermediate architectural forms exhibiting dual papillary and solid architecture were identified. Proliferation kinetics were evaluated by enumeration of silver-staining nucleolar organizer regions and proliferating cell nuclear antigen expression. The results showed a stepwise progress in cell proliferation between histologically normal renal tubule epithelium [untreated animals, mean AgNOR score (MAS) 2.32, mean PCNA index (MPI) 0.53%; treated animals, MAS, 2.44; MPI 0.99%], dysplastic tubule epithelium (MAS, 4.15; MPI 1.65%), papillary tumours (MAS, 5.90; MPI 3.89%) and solid tumours (MAS, 6.94; MPI, 6.80%). Solid tumours as a group were significantly larger than papillary tumours and were associated with a significantly longer mean post-injection survival interval. The findings suggest that at least some solid tumours evolve from tumours exhibiting papillary architecture.