(Reuters) – Shares of Spring Bank Pharmaceuticals plummeted 26% on Wednesday after the company said it would end the development of an experimental drug to treat chronic hepatitis B virus, following the death of a patient in a mid-stage trial.

Shares of Spring Bank fell to $1.60 in premarket trade. Earlier the stock was halted on the news.

The drug developer said the “occurrence of unexpected serious adverse events, including one patient death” while testing the drug, inarigivir soproxil, led to its decision.

The company said it would not pursue further research and development efforts in chronic hepatitis B virus.

“We will continue to work in close collaboration with external experts and our clinical study investigators to better understand the unexpected serious adverse events observed in our Phase 2b program,” said Martin Driscoll, the company’s chief executive officer.

The company in December had suspended the mid-stage trial that was testing the drug after laboratory findings revealed three patients showed evidence of liver dysfunction and elevation of alanine transaminase.

The company also said it will not invest in further resources towards the company’s chimeric oligonucleotide antisense (CASO) program for HBV, which it was developing in tandem with National Institute of Allergy and Infectious Diseases.

Oligonucleotide antisense is a therapeutic agent to silence specific genes at the posttranscriptional level.

Spring Bank said it has started discussions with external parties for licensing the CASO program.

(Reporting by Trisha Roy in Bengaluru; Editing by Shailesh Kuber, Bernard Orr)