Compass Therapeutics’ stock dropped after the company reported negative overall survival (OS) results tied to its bispecific antibody in a Phase 2/3 trial of second-line biliary tract cancer. The company had previously described positive activity on delayed tumor progression in an earlier readout, but investors focused on OS as the key endpoint. The latest disclosure underscores how late-line oncology programs can pivot quickly once survival data fails to confirm clinical benefit. Compass will now assess how to proceed with the program, including endpoint strategy and any potential subgroup analysis. Market reaction suggests that survival-risk assessments remain a primary determinant of valuation for bispecific oncology assets.