Gritstone bio, Inc. announced positive preliminary data from the ongoing, signal seeking Phase 2 portion of the Phase 2/3 study evaluating GRANITE, its personalized neoantigen cancer vaccine, in front-line metastatic microsatellite stable colorectal cancer (MSS-CRC). The randomized, controlled, open-label study is designed to quantify the clinical benefit of maintenance therapy with GRANITE (GRT-C901/GRT-R902) in combination with immune checkpoint blockade in addition to fluoropyrimidine/bevacizumab versus fluoropyrimidine/bevacizumab alone. Overall progression free survival (PFS) data show an early trend in benefit for GRANITE patients (HR=0.82, [95% CI, 0.34-1.67; 62% censored) and extended PFS benefit in high-risk patients (HR=0.52 [95% CI, 0.,15-1.38; 44% censored), in whom progression occurs faster.

Circulating tumor DNA (ctDNA) analysis over several months of treatment shows the expected relationship with disease progression and favors GRANITE, while short-term ctDNA response analysis (molecular response as defined per protocol) did not demonstrate a difference between study arms. Gritstone bio successfully manufactured GRANITE product candidate for every eligible patient (i.e., 100% vaccine manufacturing success rate). Thirty-six patients have left the study prior to randomized treatment primarily due to early progressive disease or withdrawal of consent, and one patient has yet to begin study treatment start. Demographics and clinical characteristics were balanced between arms (stage,sidedness, presence of liver metastases), with approximately 75% of patients having liver metastases.