The results of the phase II IMvigor 210 study demonstrated sthat previously-untreated patients taking Tecentriq lived an average of nearly 15 months.
Of those people who responded, 75% continued to respond to treatment and the median duration of response had not been reached at the time of analysis.
Seven percent of the people achieved a complete response and the median overall survival was 14.8 months.
Roche said the safety profile of Tecentriq was consistent with that observed in earlier analyses of the trial, as well as in other studies of Tecentriq as a monotherapy.
Roche chief medical officer and head of global product development Sandra Horning said: "These Tecentriq results are highly encouraging because about half of all people with this type of bladder cancer are not able to tolerate a cisplatin-based chemotherapy, and alternative treatments bring very limited duration of response.
"We are particularly pleased that the majority of people who responded to Tecentriq continued to respond at the time of analysis."
Tecentriq is designed to target and bind to a protein called programmed death ligand-1 (PD-L1), which is expressed on tumour cells and tumour-infiltrating immune cells.
PD-L1 interacts with PD-1 and B7.1, which are identified on the surface of T cells, leading to inhibition of T cells.
By blocking the interaction, Tecentriq may allow the activation of T cells, restoring their ability to identify and attack tumour cells.