On September 30, 2024, Gritstone bio, Inc. (the "Company") reported interim data from the Phase 2 portion of its randomized, open-label Phase 2/3 study evaluating its personalized cancer vaccine, GRANITE (GRTC901/GRT-R902), in combination with immune checkpoint blockade for patients with front-line metastatic microsatellite stable colorectal cancer ("MSS-CRC") (Press release, Gritstone Bio, SEP 30, 2024, View Source [SID1234646976]).
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Key Findings from Interim Phase 2 Data in MSS-CRC
Data cut as of August 19, 2024
104 patients were randomized 1:1 in the study: 69 patients (39 GRANITE arm, 30 control arm) are included in the treated analysis below. Demographics and clinical characteristics were balanced between arms (stage, sidedness, presence of liver metastases), with the vast majority (80%) of patients having liver metastases in the treated analysis. Thirty-five patients did not advance to study treatment after oxaliplatin, most commonly due to withdrawing consent (n=15), disease progression (n=8), and other reasons (n=12) (12 in GRANITE arm; 23 in control arm).
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Interim data demonstrated an emerging progression-free survival ("PFS") benefit to all GRANITE recipients (study not statistically powered for PFS)
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21% relative risk reduction of progression or death with GRANITE vs. standard of care ("SOC") control in all treated population (HR=0.79 [95% CI, 0.42-1.s])
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33% (13/39) GRANITE and 23% (7/30) of control patients remain on study and free of progression
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Last circulating tumor DNA ("ctDNA") assessment is below the assay limit of quantitation in 12/13 GRANITE and 4/7 control patients
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Clinical benefit was most notable in patients with low disease burden (defined as patients with ctDNA equal to or below the trial population median value at study entry)
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38% relative risk reduction of progression or death with GRANITE vs. SOC control with low ctDNA subgroup (HR=0.62 [95% CI, 0.23-1.70])
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Low baseline ctDNA is a likely prognostic and predictive factor
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Immune data were consistent with clinical activity
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Functional neoantigen-specific T cells were observed in all 16/16 GRANITE patients tested by ELISPOT
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Association of PFS and peak ex vivo ELISPOT responses was apparent, suggesting that ex vivo ELISPOT may be a surrogate for PFS
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GRANITE demonstrated a favorable safety and tolerability profile
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No patients discontinued study treatment due to an adverse event ("AE")
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Common AEs were the mild systemic and local effects associated with any potent vaccine, i.e. transient flu-like illness
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One treatment-related serious AE (fatigue) occurred in the GRANITE arm (patient continued GRANITE treatment without recurrence upon recovery)
The Company plans to review the PFS data with the U.S. Food and Drug Administration in the coming months and agree on next steps to advance GRANITE, including a potential Phase 2 or 3 trial using ctDNA levels as eligibility criteria.