A 49-year-old male who is a long-term smoker presents with frequency and hematuria. Histologic examination of sections taken from an exophytic lesion of the urinary bladder reveal groups of atypical cells with frequent mitoses forming finger-like projections that have thin, fibrovascular cores. These groups of atypical cells do not extend into the lamina propria and muscularis. No glands or keratin production are found. What is the most accurate diagnosis for this bladder tumor?