Shares of Bolt Biotherapeutics (BOLT -2.74%) crashed 55.8% on Monday. The steep decline came after the company presented interim data from a phase 1/2 study evaluating BDC-1001 at the European Society for Medical Oncology Immuno-Oncology (ESMO I-O) Congress that's being held virtually this week.
Bolt stated that the results were "encouraging." The company reported that early signs of clinical activity were observed in 13 out of 40 evaluable patients with advanced HER2-expressing solid tumors.
So why did the biotech stock plunge? While Bolt said that several participants achieved stable disease, only one had a durable partial response maintained through 52 weeks.
Investors were clearly disappointed with Bolt's interim results. But there were some positive takeaways from the phase 1/2 data.
The participants in the study have so far been treated with increasing dose levels of up to 20 mg/kg (or 20 mg for each kilogram of the patient's weight) every three weeks initially, then 12 mg/kg doses every two weeks. It's possible that more-frequent dosing could provide additional clinical benefit.
Bolt also pointed to the favorable safety profile of BDC-1001. There were no dose-limiting toxicities observed nor any indication of cytokine release syndrome. The adverse events that were seen have been mild infusion-related reactions thus far.
Bolt Biotherapeutics chief medical officer Edith Perez said that the company hopes to move forward with exploring weekly dosing as it draws closer to determining a dosage for BDC-1001 as a monotherapy. The drugmaker also plans to initiate a study of BDC-1001 in combination with checkpoint inhibitor Opdivo.