Cogent Biosciences announces updated data from ongoing Phase 2 APEX trial

Cogent Biosciences (COGT) reported positive updated data from Part 1 of the company’s ongoing Phase 2 APEX clinical trial evaluating bezuclastinib in patients with advanced systemic mastocytosis at the 66th American Society of Hematology Annual Meeting & Exposition taking place December 7-10, 2024 in San Diego, CA. As of the data cutoff date of October 11, 2024, 32 patients enrolled were evaluated for signs of clinical activity, 27 of whom were mIWG-MRT-ECNM evaluable. Clinical activity analyzed across dose levels and focused on 100 mg BID cohort showed: 52% ORR per mIWG-MRT-ECNM criteria, including 61% ORR for TKI-treatment-naive patients; 83% ORR for patients treated at 100 mg BID dose cohort; 88% ORR per pure pathological response criteria; 100% ORR for patients treated at 100 mg BID dose cohort; Median time to achieve response was 2.2 months and median duration of response has not yet been reached; Median PFS was not yet reached at median follow-up of 20 months; PFS rate at 24 months was 82%. Nearly all patients demonstrated a significant improvement in biomarkers associated with disease burden. Patients without post baseline biomarker data were excluded from relevant analyses. 94% of patients achieved greater than or equal to 50% reduction in serum tryptase levels. 100% of patients receiving greater than or equal to2 cycles achieved greater than or equal to 50% reduction. 66% of patients achieved reduction of serum tryptase below 20 ng/mL. 93% of KITD816V-positive patients achieved greater than or equal to50% reduction in KIT D816V variant allele fraction. 100% of evaluable patients achieved a greater than or equal to50% reduction in bone marrow mast cell burden. 83% achieved complete clearance of mast cell aggregates by central review. As of the data cutoff date of October 11, 2024, bezuclastinib continues to demonstrate a differentiated safety and tolerability profile across doses. Due to confounding medical issues, one patient previously reported with DILI has been reassessed and reported as a Grade 4 gamma-glutamyl transferase elevation case. Twelve patients required dose reduction, eight of whom were treated at a 400 mg daily dose.