Time to metastasis predicts prognosis and improves the Bellmunt score in metastatic urothelial carcinoma

Technical Summary: Time to Metastasis as a Prognostic Factor in Metastatic Urothelial Carcinoma

Problem Statement
Metastatic urothelial carcinoma (mUC) carries a poor prognosis, with 5-year survival rates ranging from 5% to 15%. While prognostic models such as the Bellmunt score exist to stratify risk, they rely on established clinical factors (hemoglobin levels, ECOG performance status, and liver metastasis) and demonstrate limited accuracy. The timing of metastasis relative to initial diagnosis—specifically Time to Metastasis (TTM)—is a recognized prognostic variable in other urologic malignancies like metastatic renal cell carcinoma and prostate cancer. However, its specific significance and utility in risk stratification for mUC remain unclear and under-evaluated.

Methodology
The authors conducted a retrospective, multicenter study involving 388 patients with mUC who received first-line platinum-based chemotherapy between April 2009 and May 2025. Data were drawn from the Hiroshima Cancer Registry Project (H-CARP).

• Cohort Definition: Patients were categorized based on TTM into two groups: synchronous metastasis (TTM < 6 months) and metachronous metastasis (TTM ≥ 6 months).
• Endpoints: The primary endpoint was Overall Survival (OS), defined as the time from the initiation of first-line chemotherapy to death from any cause.
• Statistical Analysis: The study employed univariate and multivariate Cox proportional hazards regression to identify independent predictors of OS. To evaluate the utility of adding TTM to existing models, the authors compared the original Bellmunt score against a modified Bellmunt score (incorporating TTM). Performance was assessed using:
  • Harrell's concordance index (C-index) for discrimination.
  • Time-dependent C-indices at 12 and 24 months.
  • Decision Curve Analysis (DCA) for net clinical benefit.
  • Net Reclassification Improvement (NRI) to measure risk reclassification accuracy.

Key Contributions

1. Validation of TTM: The study establishes TTM as an independent prognostic factor for OS in mUC, confirming that synchronous disease is associated with significantly worse outcomes compared to metachronous disease.
2. Development of a Modified Risk Model: The authors propose a modified Bellmunt score that integrates TTM alongside the traditional factors (hemoglobin < 10 g/dL, ECOG-PS ≥ 1, and liver metastasis).
3. Risk Stratification Refinement: The new model defines four risk groups (good, intermediate, poor, and very poor) based on the cumulative number of adverse factors, offering a more granular approach to patient stratification.

Results

• Patient Characteristics: Of the 388 patients, 266 (68.6%) had synchronous metastasis and 122 (31.4%) had metachronous metastasis. The synchronous group exhibited significantly lower hemoglobin levels, higher rates of lymph node metastasis, and lower rates of prior cystectomy/nephroureterectomy compared to the metachronous group.
• Survival Analysis: Kaplan-Meier analysis revealed significantly poorer OS for the synchronous group (p = 0.001).
• Multivariate Findings: In the multivariate analysis, three factors were identified as independent predictors of shorter OS:
  • Liver metastasis (HR: 3.32, p < 0.001)
  • Hemoglobin < 10 g/dL (HR: 1.66, p = 0.008)
  • Synchronous metastasis (HR: 1.69, p = 0.016)
• Model Performance: Incorporating TTM into the Bellmunt score significantly improved prognostic performance:
  • The overall C-index increased from 0.575 (original) to 0.613 (modified).
  • Time-dependent C-indices were superior for the modified score at both 12 months (0.639 vs. 0.596) and 24 months (0.692 vs. 0.648).
  • Decision Curve Analysis demonstrated a greater net clinical benefit for the modified score across a wide range of threshold probabilities.
  • Net Reclassification Improvement (NRI) was statistically significant (0.075), driven primarily by the event-NRI, indicating the model successfully reclassified patients who experienced events into higher-risk categories.

Significance and Claims
The paper claims that Time to Metastasis is a clinically meaningful and independent prognostic factor for patients with metastatic urothelial carcinoma. By incorporating TTM into the established Bellmunt score, the authors demonstrate a statistically significant improvement in risk stratification accuracy. The modified model offers a more refined framework for predicting survival, potentially aiding clinicians in better identifying high-risk patients. The authors note that while the 6-month cutoff for TTM was chosen based on prior literature and internal analysis showing no survival difference between 0 and 6 months, further investigation is needed to determine the optimal threshold. They also acknowledge limitations, including the retrospective nature of the study, lack of external validation, and the exclusion of patients receiving newer combination therapies (e.g., enfortumab vedotin plus pembrolizumab), suggesting the findings should be applied with consideration of the evolving treatment landscape.