Outcome Analysis of a Series of Mixed-Grade, Non-muscle Invasive, Papillary Carcinomas of the Bladder

Introduction. Papillary urothelial carcinomas are currently graded as either low- or high-grade tumors based on World Health Organization (WHO) 2022 guidelines for genitourinary tumors. However, a minority of tumors are mixed-grade tumors, composed predominantly of low-grade cancer with a minor high-grade component. In the 2022 WHO these cancers are recognized as having outcomes comparable to low-grade cancers, although data to date has been limited. Methods. The pathology records of a large academic institution were searched for mixed-grade, non-muscle invasive papillary carcinomas of the bladder and ureter in order to characterize prognosis of these cancers. Results. Of 136 cancers, the majority (n = 104, 76.5%) were solitary, mixed-grade tumors, while 21 (15.4%) had a concurrent low-grade cancer and 11 (8.1%) had multiple mixed-grade tumors at the time of diagnosis. At follow-up (median 48.3 months, range = 1.3 months-18.1 years), 71 cancers recurred (52.2%): 52 (38.2%) as low- or mixed-grade cancers and 18 (13.2%) as high-grade cancers. There were no instances of stage-progression to >= pT2. Conclusions. The clinical outcome of mixed-grade carcinomas was similar to what has been reported for low-grade carcinomas. Based on our results, and prior congruent studies of mixed-grade lesions, these lesions may be regarded as a distinct sub-category with a better prognosis than high-grade tumors.