NRAS and neoplasm: To assess if loss of progressively more Ras alleles alters tumor progression, tumors developing in Hras+/+;Nras+/+ control mice, Hras-/-;Nras+/+ mice lacking Hras, Hras+/+;Nras-/- mice lacking Nras, or Hras-/-;Nras-/- mice lacking both Hras and Nras were graded in a blinded fashion by 2 pathologists.