Gritstone bio (GRTS.Q) Status Update summary

Program overview and clinical context

• Lead program GRANITE is a personalized neoantigen immunotherapy in phase II for metastatic microsatellite stable (MSS) colorectal cancer, with mature PFS data expected this quarter and OS data in mid-2025.

• GRANITE targets a major unmet need, as most MSS colorectal cancer patients do not benefit from checkpoint inhibitors, unlike the small MSI-high subgroup.

• The approach uses AI to identify neoantigens and delivers them via a heterologous prime-boost vaccine system, combined with checkpoint inhibitors.

• The phase II trial randomizes patients to standard maintenance chemotherapy or chemotherapy plus the neoantigen vaccine, atezolizumab, and low-dose ipilimumab.

• The pivotal phase III study is planned for next year, pending positive phase II results, with PFS or OS as the likely primary endpoint.

Patient and advocacy perspectives

• Patient advocates emphasize the severe impact of colorectal cancer on quality of life, the need for new therapies, and the importance of patient education and involvement.

• Current standard chemotherapies are decades old, have significant side effects, and often fail to provide durable benefit.

• Advocacy groups like ColonTown and the Colorectal Cancer Alliance are actively shaping research priorities and supporting patients.

• Survivorship remains rare in advanced MSS colorectal cancer, highlighting the urgency for innovative treatments.

Unmet need and treatment landscape

• Colorectal cancer is the second leading cause of cancer death globally, with rising incidence in younger adults.

• Most advances in treatment occurred in the early 2000s; since then, progress has stagnated, especially for MSS disease.

• First-line therapy relies on old chemotherapies, with modest improvements in survival and significant toxicity.

• Only 3-5% of patients (MSI-high) benefit from immunotherapy; the vast majority (MSS) have limited options.