IBCN 2023: Long Term Recurrence Risk, Metastatic Potential, and Length of Surveillance of Low Grade Non-Muscle Invasive Bladder Cancer

(UroToday.com) Historically, very few patients with Ta low grade (LG) bladder cancer (BC) are at risk of developing metastases or dying of BC. However, long term follow-up data are scant and length of follow-up is poorly defined, especially when free of recurrence for 5 years. They investigated the incidence of late "recurrence", risk of metastases, and death due to BC in patients with TaLG BC.

This retrospective study analyzed 521 patients with primary TaLG diagnosed between 1989-2019 at a university center (Toronto, Canada). Risk of recurrence, progression to high grade Ta/T1, muscle invasion, metastases, and death due to BC at 5, 10, and 15 years were assessed. RNAseq analysis compared the transcriptomic profiles of 4 LG tumors that metastasized to non-progressing tumors. Inter-observer variability in pathological grade by expert pathologists was assessed in 80 cases.

The mean and median follow-up was 9.9 and 8.5 years, respectively. Among 521 patients (72.9% men, median age 67.0 years), 350(67.2%) recurred, 57(10.9%) progressed in stage, 20(3.8%) developed metastases and 15(2.9%) died from BC.

Of the patients recurrence-free for the first 5 years, 50 (50/251, 9.6%) developed BC within 20 years and 2 died of BC (2/521, 0.4%). Cancer specific survival was 99.1%, 97.8%, and 96.3% at 5, 10, and 15 years, respectively. Transcriptomic profiles between metastasized Ta LG and nonrecurring tumors were different, despite appearing phenotypically similar. Moderate concordance was observed using the 1973 WHO grading system (Kappa=0.41;95%CI=0.32-0.50), improved with the 2004 system (0.78; 95%CI=0.65-0.90).

These results challenge the assumption that LG Ta BC nearly never progress to potentially lethal disease, with 2.9% dying from BC. However, the risk of BC-related mortality is extremely low in patients recurrence-free for the first 5 years. Efforts are needed to minimize inter-observer variability in pathological grading as surprisingly even experts sometimes disagree between low and high grade.

Presented by: Amy Chan, Division of Urology, Department of Surgery, Mount Sinai Hospital, Sinai Health System, Toronto, ON, Canada

Written by: Stephen B. Williams, MD, MBA, MS @SWilliams_MD on Twitter during the International Bladder Cancer Network (IBCN) Annual Meeting, September 29-30, 2023, Montreal, Canada