(UroToday.com) The 2024 IBCN annual meeting included a bladder cancer session, featuring a presentation by Dr. Amy Chan discussing influence of immortal time bias and conditional survival on the comparison of radical cystectomy versus trimodality therapy for muscle invasive bladder cancer. Dr. Chan and colleagues recently demonstrated, in a multi-institutional propensity score matched and weighted analysis study, similar oncological outcomes between radical cystectomy and trimodality therapy for select patients with muscle-invasive bladder cancer [1]. Despite using propensity score matching and inverse probability treatment weighting (IPTW) to balance groups when a randomized study is not available, inherent confounding variables and biases can persist. At IBCN 2024, Dr. Chan investigated the impact of immortal time bias as well as conditional survival on outcomes.
This retrospective analysis included 722 patients with clinical stage T2–T4N0M0 muscle-invasive bladder cancer (440 radical cystectomy, 282 trimodality therapy), solitary tumors <7 cm, no or unilateral hydronephrosis, and no extensive CIS, who would have been eligible for both approaches. The investigators analyzed the data comparing radical cystectomy versus trimodality therapy to exclude immortal time bias as radical cystectomy patients are at immediate postoperative risk in contrast to trimodality therapy which is delivered on a 6 ½ week period. The primary endpoint was metastasis-free survival, and secondary endpoints included overall survival, disease-free survival, and cancer-specific survival. Differences in survival outcomes were analyzed using propensity score matching with 3:1 matching, and IPTW. Conditional survival probabilities were calculated for patients event-free at 1, 2, 3, 4, and 5 years.
Taking into account immortal time, there was no difference between trimodality therapy versus radical cystectomy in metastasis-free survival (HR for IPTW and propensity score matching, 0.92, 95% CI 0.68, 1.23, p = 0.56, and HR 0.95, 95% CI 0.72, 1.25, p = 0.70, respectively):
Additionally, there was no difference in disease-free survival (HR for IPTW and propensity score matching 0.89, 95% CI 0.67, 1.19, p = 0.60, and HR 0.92, 95% CI: 0.70, 1.21, p = 0.56, respectively) and cancer-specific survival (HR for IPTW and propensity score matching, 0.74, 95% CI: 0.52, 1.06, p = 0.10, and HR 0.73 95% CI 0.52, 1.03, p = 0.07, respectively). For overall survival, HR for IPTW and propensity score matching favored trimodality therapy (HR 0.73, 95% CI 0.55, 0.96, p = 0.02, and HR 0.75, 95% CI 0.59, 0.64, p = 0.03, respectively):
Analyzing conditional survival comparing overall survival, metastasis-free survival, cancer-specific survival, and disease-free survival, all p values at 1, 2, 3, 4, or 5 years did not reach statistical significance.
Dr. Chan concluded her presentation by discussing the influence of immortal time bias and conditional survival on the comparison of radical cystectomy versus trimodality therapy for muscle invasive bladder cancer by emphasizing that even after taking into account potential biases due to immortal time bias and re-analyzing the data with conditional survival, this multi-institutional study showed similar oncological outcomes between radical cystectomy and trimodality therapy for select patients with muscle-invasive bladder cancer.
Presented by: Amy Chan, Mount Sinai Hospital, Toronto, Ontario, Canada
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Associate Professor of Urology, Georgia Cancer Center, Wellstar MCG Health, @zklaassen_md on Twitter during the 2024 International Bladder Cancer Network (IBCN) Annual Meeting, Bern, Switzerland, Thurs, Sept 19 – Sat, Sept 21, 2024
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