Seattle Genetics plunges as FDA slaps clinical hold on several drug trials

US biotech firm Seattle Genetics (Nasdaq: SGEN) saw its shares down almost 16% at $52.04 on Tuesday morning, after it revealed receipt of a notice from the US Food and Drug Administration that a clinical hold or partial clinical hold has been placed on several early stage trials of vadastuximab talirine (SGN-CD33A) in acute myeloid leukemia (AML).

The clinical holds were initiated to evaluate the potential risk of hepatotoxicity in patients who were treated with SGN-CD33A and received allogeneic stem cell transplant either before or after treatment. Six patients have been identified with hepatotoxicity, including several cases of veno-occlusive disease, with four fatal events. Overall, more than 300 patients have been treated with SGN-CD33A in clinical trials across multiple treatment settings. Seattle Genetics is working with the FDA to determine whether there is any association between hepatotoxicity and treatment with SGN-CD33A, to promptly identify appropriate protocol amendments for patient safety and to enable continuation of these trials.

The Phase I/II trial of SGN-CD33A monotherapy in pre- and post-allogeneic transplant AML patients has been placed on full clinical hold. Two Phase I trials have been placed on partial clinical hold (no new enrollment, existing patients may continue treatment with re-consent). These studies are SGN-CD33A monotherapy, including a subset of older AML patients in combination with hypomethylating agents, and SGN-CD33A combination treatment with 7+3 chemotherapy in newly diagnosed younger AML patients. No new studies will be initiated until the clinical holds are lifted.