Gritstone Cancer Vaccine Trial Misses Primary Endpoint, Stock Plummets

1. Gritstone's Phase 2 cancer vaccine trial aimed at treating metastatic microsatellite stable colorectal cancer did not achieve its primary endpoint, which focused on changes in circulating tumor DNA (ctDNA).
2. The trial included 104 patients, where half received Gritstone's personalized neoantigen cancer vaccine along with Bristol Myers Squibb's Yervoy and Roche's Tecentriq during the maintenance phase.
3. The primary endpoint measured molecular responses based on ctDNA, which resulted in a numerical advantage for the chemotherapy-alone group over the vaccine group (30% vs. 41.7%) due to Gritstone misinterpreting how ctDNA would change post-treatment.
4. Despite missing the primary endpoint, Gritstone highlighted early trends favoring the vaccine in terms of progression-free survival (PFS). However, these PFS findings were considered immature and lacked statistical significance.
5. Gritstone expected mature PFS data in Q3 2024 and overall survival (OS) data in the first half of 2025.
6. Following the update, Gritstone's stock experienced a sharp decline, with shares losing approximately 33% in after-hours trading.
7. The company faced financial challenges, having about $79.2 million in cash at the end of September 2023, and subsequently raised about $33 million through a secondary stock offering.