I n 1973, Dr. F. K. Mostofi proposed a three-tiered system (World Health Organization [WHO] Grades 1, 2, and 3) to grade urothelial (transitional cell) carcinoma of the urinary bladder. 1 Grading was based on the degree of anaplasia of tumor cells, which was defined as increased cellularity, nuclear crowding, disturbance of cellular polarity, failure of differentiation from the base to the surface, polymorphism, irregularity in cell size, variations of shape and chromatin pattern of the nuclei, displaced or abnormal mitotic figures, and giant cells. The presence of any degree of anaplasia (such as increased cellularity) in any papillary lesions (except papillary cystitis) should lead to a diagnosis of carcinoma. 1 Grade 1 urothelial carcinoma was defined as tumors that have the least degree of cellular anaplasia; Grade 3 carcinoma has the most severe degrees of cellular anaplasia; and Grade 2 carcinoma lies in between. 1 By definition, papilloma was a papillary tumor with a delicate fibrovascular stroma lined by cytologically and architecturally normal urothelium without increased cellularity or mitotic figures.
The diagnosis of carcinoma may have a significant bearing on the patients and the society. Some pathologists are concerned about labeling a low grade noninvasive tumor as carcinoma. The term "papillary urothelial neoplasm of low malignant potential (LMP)" was introduced in the 1998 World Health Organization and International Society of Urological Pathology (WHO/ISUP) classification. 2 Recognizing that high levels of inter-and intraobserver variability of histologic grading exist, the definition and histologic criteria for grading (LMP, low grade, and high grade) were further refined and described