Roche Holding said it had temporarily suspended recruitment of patients into a clinical trial assessing the use of colon cancer drug Avastin after surgery because of a number of deaths.
Roche stock fell 1.1 per cent on concerns about the drug's sales prospects in the important adjuvant, or post-surgical, setting.
The trial is designed to see how patients fare when given either conventional chemotherapy drugs or an Avastin-based combination.
Despite the move, the Swiss drugmaker said its broad oncology programme, which it is working on with Genentech, remained on track.
Avastin belongs to a new generation of medicines that work by starving tumours of the blood supply they need to grow. It has been hugely successful for both Roche and Genentech, in which Roche holds a majority stake.
The temporary suspension of the study was called for by the trial's safety monitoring board following four sudden deaths in one of the three study arms, which involved patients taking Avastin plus the chemotherapy treatment XELOX.