Nature of unfavorable histologic features:
(1) reflect resistance to therapy rather than more aggressive growth
(2) are significant in Stages II to V; they do not apply to Stage I lesions.
(3) are rare during the first 2 years of life but increase with age afterwards
(4) may be focal or diffuse; thorough sampling may be required to identify localized areas
Unfavorable histologic features:
(1) nuclear anaplasia
(2) high grade renal cell carcinoma
(3) high p53 nuclear expression
Nuclear anaplasia in blastematous elements, as indicated by all 3 of the following:
(1) abnormal mitotic figures, markedly enlarged and often multipolar; each "arm" is longer than that of a normal metaphase
(2) nuclei with a maximum diameter >= 3 times greater than the diameter of nuclei in adjacent cells of the same cell type
(3) hyperchromasia of the enlarged nuclei
