NuCana (NASDAQ:NCNA) ADRs plunged ~50% on Friday after the British biotech announced its decision to discontinue a Phase 2 trial for its colorectal cancer therapy NUC-3373, based on data from an initial analysis.

On Thursday evening, Edinburgh-based NuCana (NCNA) said that its NuTide:323 Study for a combination therapy involving NUC-3373 was unlikely to reach its primary objective of progression-free survival in patients with colorectal cancer.

As a result, the company said that the trial’s steering committee has recommended an early end to the trial.

The three-arm study was designed to evaluate NUC-3373 as part of a combination regimen involving the folic acid derivative, leucovorin plus irinotecan and bevacizumab, anticancer treatments marketed by Pfizer (PFE) and Roche (OTCQX:RHHBY) (OTCQX:RHHBF) as Camptosar and Avastin, respectively.

As for safety, the company said 12 out of 175 patients (four in each arm) discontinued the treatment due to adverse events.

NuCana (NCNA) added that the results will not impact the NuTide:303 study, in which NUC-3373 is tested with either Merck’s (MRK) Keytruda in solid tumors or chemotherapy docetaxel in lung cancer.

However, William Blair argued that with NuTide:323 being the first controlled trial for NUC-3373, the company would struggle to regain investor interest from other trials in the program. The firm downgraded NuCana (NCNA) to Market Perform from Outperform.