To describe the natural history of untreated muscle-invasive bladder cancer (MIBC) and compare the oncological outcomes of treated and untreated patients.

We utilised a database encompassing all patients with newly diagnosed bladder cancer in Stockholm, Sweden between 1995 and 1996. The median follow-up for survivors was 14.4 years. Overall, 538 patients were diagnosed with bladder cancer of whom 126 had clinically localised MIBC. Patients were divided into two groups: those who received radical cystectomy or radiation therapy, and those who did not receive any form of treatment. Multivariable Cox or competing-risks regressions were adopted to predict metastasis, overall survival (OS), and cancer-specific mortality (CSM), when appropriate. Analyses were adjusted for age at diagnosis, sex, tumour stage, clinical N stage, and treatment.

In all, 64 (51%) patients did not receive any definitive local treatment. In the untreated group, the median (interquartile range) age at diagnosis was 79 (63-83) vs 69 (63-74) years in the treated group (P < 0.001). Overall, 109 patients died during follow-up. At 6 months after diagnosis, 38% of the untreated patients had developed metastatic disease and 41% had CSM. The 5-year OS rate for untreated and treated patients was 5% (95% confidence interval [CI] 1, 12%) vs 48% (95% CI 36, 60%), respectively. Patients not receiving any treatment had a 5-year cumulative incidence of CSM of 86% (95% CI 75, 94%) vs 48% (95% CI 36, 60%) for treated patients. Untreated patients had a higher risk of progression to metastatic disease (hazard ratio [HR] 2.40, 95% CI 1.28, 4.51; P = 0.006), death from any cause (HR 2.63, 95% CI 1.65, 4.19; P < 0.001) and CSM (subdistribution HR 2.02, 95% CI 1.24, 3.30; P = 0.004).

Untreated patients with MIBC are at very high risk of near-term CSM. These findings may help balance the risks vs benefits of integrating curative intent therapy particularly in older patients with MIBC.