AnaptysBio Inc (ANAB) saw its stock price plummet by 19.29% in pre-market trading on Monday following the announcement that its Phase 2 clinical trial for rosnilimab in ulcerative colitis patients failed to meet its primary and secondary endpoints. This significant drop reflects investor disappointment in the potential of one of the company's key drug candidates.

The global Phase 2 clinical trial evaluated rosnilimab in patients with moderate-to-severe ulcerative colitis. While the drug was found to be safe and well-tolerated, with adverse event rates similar to placebo, it did not achieve the primary endpoint of mean change from baseline in modified Mayo Score. Additionally, the trial failed to meet key secondary endpoints of clinical response and clinical remission at Week 12. As a result of these disappointing outcomes, AnaptysBio has made the decision to discontinue the ulcerative colitis trial.

This setback is likely to have significant implications for AnaptysBio's pipeline and future prospects. However, the company is not abandoning rosnilimab entirely. AnaptysBio plans to provide an update in the first half of 2026 on the advancement of rosnilimab for rheumatoid arthritis, indicating a shift in focus for the drug candidate. The discontinuation of the ulcerative colitis trial is expected to result in savings of at least $10 million for the company. Despite this negative news, Truist Securities has adjusted their price target for AnaptysBio from $20 to $36, maintaining a Hold rating, suggesting that some analysts still see potential in the company's overall portfolio.