Introduction:

Metastatic non-muscle invasive bladder cancer (mNMIBC) is a condition in which bladder cancer patients develop metastases in the absence of muscle invasion. The nature of mNMIBC is relatively new and largely underexplored. The objective of our study was to analyze the baseline characteristics, metastatic patterns, and survival outcomes of this condition in comparison with muscle-invasive bladder cancer (MIBC) with metastasis.

Methods:

Data from patients diagnosed with mNMIBC and MIBC with metastases between 2004 and 2021 were analyzed for patient characteristics, survival outcomes, and metastatic trends. Demographic and clinical variables were compared using the Chi-square and Fisher’s exact analysis. Survival outcomes between the two patient cohorts were compared based on the site of metastasis and histology subtypes. Kaplan-Meier analysis was also performed to compare survival outcomes.

Results:

Of 826,983 bladder cancer patients, 22,432 had metastasis. Among them, 3,982 patients were in the NMIBC group, and 18,450 patients had metastasis in the MIBC group. The single most common sites of known metastasis in both groups were bone, followed by lung, liver, and brain. Furthermore, 15.1% of patients in mNMIBC and 13.5% of patients in MIBC with metastasis had multiple metastases. The median overall survival (OS) of mNMIBC and MIBC with metastasis was 6.54 (6.04 – 7.03) months and 6.24 (6.08 – 6.39) months, respectively (p < 0.001). The OS was poor in cases with metastasis to multiple sites [median OS: 3.55 (3.05 – 4.04) months in mNMIBC and 4.04 (3.78 – 4.29) months in MIBC with metastasis (p < 0.001)] in comparison to all other isolated metastases. The best OS in isolated metastasis was seen in lung metastasis [median OS: 8.48 (6.68 – 10.27) months] in mNMIBC and bone metastasis [median OS: 6.90 (6.45 – 7.35) months in MIBC with metastasis] (p < 0.001). The worst OS was seen in liver metastasis [median OS: 3.70 (2.80 – 5.59) months] in mNMIBC and brain metastasis in MIBC with metastasis [median OS: 5.13 (4.03 – 6.23) months] (p < 0.001). The most common histology in both groups was urothelial carcinoma, followed by small cell carcinoma, squamous cell carcinoma, and adenocarcinoma.

Conclusion:

mNMIBC is a relatively uncommon (0.74% of NMIBC) condition that has poor survival outcomes [median OS: 6.54 months], which is similar to MIBC with metastasis [median OS: 6.24 months]. Metastases to multiple sites have a poorer prognosis (median OS: 3.55 months in mNMIBC and 4.04 months in MIBC with metastasis) than metastasis to a single site. Among the isolated metastases, the single most common metastatic site was bone in both groups. However, the best OS was seen in lung metastasis (median: 8.48 months) in mNMIBC group and bone metastasis (median OS: 6.54 months) in the MIBC group.

Funding: N/A