Shares of Compass Therapeutics Inc. (CMPX) are down more than 63% in pre-market trading despite the company reporting that its investigational antibody Tovecimig achieved a highly statistically significant improvement in progression-free survival in the COMPANION-002 Phase 2/3 study in biliary tract cancer.
The company said the results reinforce Tovecimig's potential to address a major unmet need in patients with limited treatment options.
Biliary tract cancer is an aggressive and rare cancer with poor survival outcomes, especially for patients whose tumors do not carry actionable mutations. In the second-line setting, available therapies typically produce response rates of around 5% and median overall survival of roughly six months.
Statistically significant improvement in PFS
In the randomized COMPANION-002 study Tovecimig- a DLL4 x VEGF-A bispecific antibody- was evaluated in combination with paclitaxel versus paclitaxel alone. The combination achieved a median PFS of 4.7 months, compared with 2.6 months for paclitaxel alone, representing a 56% reduction in the risk of disease progression (hazard ratio 0.44; p<0.0001).
The company noted that the strong PFS benefit builds on previously announced data showing that the study met its primary endpoint of overall response rate (ORR), with a response rate of 17.1% for the Tovecimig combination versus 5.3% for paclitaxel alone.
Overall survival impacted by crossover
Overall survival (OS) did not reach statistical significance due to 54% of control-arm patients crossing over to receive Tovecimig after progression. These crossover patients had a median OS of 12.8 months, compared with 6.1 months for those who remained on paclitaxel alone.
Because 85% of all patients in the study ultimately received Tovecimig, the pooled median OS across the trial was 8.9 months, which Compass noted is longer than typical chemotherapy benchmarks of approximately six months.
Safety profile consistent with prior studies
Tovecimig was generally well tolerated, with no new safety signals observed. The most common treatment-emergent adverse events in the combination arm were hypertension (69%) and fatigue (67%). Grade 3 or higher events most frequently included hypertension (44%) and neutropenia (36%).
Next Steps
Compass plans to meet with the U.S. FDA in the coming months ahead of a planned Biologics License Application (BLA) submission. The company will present the full dataset, including duration-of-response results, at a medical conference later this year.
CMPX has traded between $1.66 and $6.88 over the past year. The stock is currently trading at $1.90, down 62.25%.
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