Gritstone bio Announces Positive Preliminary Progression-free Survival and Long-term Circulating Tumor DNA (ctDNA) Data from Phase 2 Portion of Ongoing Phase 2/3 Study of its Personalized Cancer Vaccine, GRANITE, in Front-line Metastatic Microsatellite St - Seite 2

“Today's preliminary Phase 2 results are highly encouraging and represent the first randomized trial evidence, albeit early, that a personalized neoantigen-directed vaccine can potentially drive efficacy in a metastatic ‘cold’ tumor. The overall trend of PFS improvement in GRANITE recipients is great to see, and the exploratory PFS hazard ratio of 0.52 in the high-risk group, a more mature dataset, is a striking signal,” said Andrew Allen, MD, PhD, Co-founder, President & CEO of Gritstone bio. “Pioneering new spaces carries inherent risks, and with regard to defining molecular response, we simply got it wrong. ctDNA levels in both arms decreased on chemotherapy for longer than we anticipated, generating similar short-term molecular response rates across arms and rendering our protocol measure of ctDNA change uninformative. Fortunately, long-term analysis demonstrates the expected correlation of ctDNA with clinical benefit and favors GRANITE patients. We believe these preliminary findings put us in a strong position to share mature PFS data in the third quarter and then enter regulatory discussions regarding Phase 3. The growing body of evidence favoring GRANITE in this trial, including positive PFS and long-term ctDNA trends in both high and low-risk populations, is exciting and suggests GRANITE is working in this notoriously underserved patient population.”

“Up to 97% of patients with metastatic colorectal cancer, the second most common cause of cancer death, are MSS. Unlike patients with melanoma and lung cancer, they have not benefited from standard immunotherapies such as checkpoint inhibitors. These preliminary results indicate that GRANITE is inducing a potentially significant immune response in a disease that has been felt to be immunologically cold,” said J. Randolph Hecht, MD, Professor of Clinical Medicine and Director of the UCLA GI Oncology Program and an investigator in the GRANITE Phase 2/3 study. “The PFS difference, particularly in a poor prognosis group of patients, indicates the potential for clinical benefit and provides the rationale for a confirmatory Phase 3 trial, about which I am very excited. Furthermore, we are learning how to better analyze ctDNA continuously to study the efficacy of this novel immunotherapy. Expanding the scope of immunotherapy to a broader spectrum of cancer patients is the ‘holy grail’ of oncology, especially for MSS colorectal cancer. While early, these promising results suggest GRANITE has potential to deliver clinically meaningful benefit in MSS-CRC and other cold tumors.”