Tecentriq initially won accelerated FDA approval in 2016 for people previously treated for the most common form of bladder cancer, but was required to gather follow-up data in order to win regular approval.
"This could play a role in assessing if, or when, an individual needs revaccination, or in helping to answer other clinically relevant questions," Roche said in a statement.
Roche launched the 330-patient trial in March as it joined other pharmaceutical companies seeking to re-purpose existing medicines to fight the pandemic.