Leap Therapeutics Halts Sirexatamab Combo Therapy For Gastric Cancer ON Unclear Positive Signal, Stock Crashes

On Tuesday, Leap Therapeutics, Inc. LPTX released initial data from Part B of the DeFianCe Phase 2 study of sirexatamab (DKN-01) in combination with bevacizumab and chemotherapy as a second-line treatment for advanced colorectal cancer (CRC).

The 188-patient Part B of the study showed that patients treated with sirexatamab plus bevacizumab and chemotherapy (experimental arm) had an objective response rate (ORR) of 35% and a disease control rate (DCR) of 86%, compared to an ORR of 23% and DCR of 84% in patients treated with bevacizumab and chemotherapy alone.

• Across the population with left-sided primary tumors (n=144):Patients treated in the Experimental Arm (n=71) had an ORR of 38%, compared to an ORR of 25% in the Control Arm (n=73)

Leap expects to report additional data as it matures in 2025.

Sirexatamab plus bevacizumab and chemotherapy was well-tolerated, without additive toxicity to the standard of care.

The company also released initial data from Part C of the DisTinGuish Phase 2 study of sirexatamab in combination with BeiGene Ltd’s ONC tislelizumab and chemotherapy in first-line patients with advanced gastroesophageal junction (GEJ) and gastric cancer.

While demonstrating activity in biomarker populations, the study did not generate a clear positive signal. It will be negative on the primary progression-free survival (PFS) endpoints when the study is completed, resulting in the decision not to proceed with Phase 3 studies in gastric cancer.

• Across the ITT population (n=170), patients treated with sirexatamab plus tislelizumab and chemotherapy (Experimental Arm, n=85) had a confirmed ORR of 52% by both investigator assessment (IA) and Blinded Independent Central Review (BICR), while patients treated with tislelizumab and chemotherapy alone had a confirmed ORR of 56% by IA and 42% by BICR.
• In the ITT population, the preliminary median PFS in the Experimental Arm was 9.72 months by BICR and 7.66 months by IA, compared to 11.99 months by BICR and 10.41 months by IA in the Control Arm. The median PFS for tislelizumab plus chemotherapy in the Phase 3 Rationale-305 study was 6.9 months.

Price Action: LPTX stock is down 78.80% at $0.66 at last check Tuesday.

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