Metastatic non-muscle invasive bladder cancer: histology-specific metastatic patterns and survival in a national cancer database analysis

Metastasis development in bladder cancer patients without any evidence of muscle invasion is known as metastatic non-muscle invasive bladder cancer (mNMIBC). Given its recent recognition, this condition is largely underexplored. The objective of our study was to analyze the baseline characteristics, metastatic patterns, and survival outcomes of this condition based on different histology subtypes.

Data from patients with mNMIBC were analyzed across different histology subtypes. Demographic and clinical variables were compared using Chi-square and Fisher's exact analysis. Kaplan-Meier analysis was performed to compare survival outcomes between the various types of histology.

Among the 537,674 patients diagnosed with NMIBC, 3982 had distant metastasis. The most common histopathology type was urothelial carcinoma [UC] (86.2%), followed by small cell carcinoma [SCC] (3.2%), squamous cell carcinoma [SqCC] (2.6%), adenocarcinoma (1.6%), and other variants (6.4%). The median overall survival (OS) of mNMIBC was 6.54 months. Among the various histopathology types, adenocarcinoma had the best OS (median OS: 12.71 months), followed by SCC (median OS: 8.87 months), UC (median OS: 6.83 months), and SqCC (median OS: 3.48 months). All results were statistically significant (p = 0.002). The common sites of metastasis were bone in UC (15.8%), lungs in SqCC (18.1%) and adenocarcinoma (16.9%), and liver in SCC (22%).

mNMIBC is an uncommon (0.74% of NMIBC) condition with a poor prognosis. The most common and least common subtypes were urothelial carcinoma and adenocarcinoma, respectively. In comparison with the other subtypes, adenocarcinoma had the best prognosis, and squamous cell carcinoma had the worst prognosis.