Coverage: Seattle Genetics stock plunges after FDA halts test

Shares of Seattle Genetics Inc. plummeted on Tuesday after the company said four leukemia patients died in clinical trials of an experimental treatment, prompting the U.S. Food and Drug Administration to halt, or suspend enrollment in, several studies.

Peter Loftus and Austen Hufford of The Wall Street Journal had the news:

The drug, vadastuximab talirine, is being tested to treat acute myeloid leukemia, an aggressive cancer of the blood and bone marrow. More than 300 patients have been treated with the drug so far. Vadastuximab is designed to target and destroy leukemia cells while minimizing damage to healthy cells, and had promising rates of inducing remissions in early-stage studies.

But the Bothell, Wash., company said Tuesday that six patients taking the drug have had hepatotoxicity, or liver damage, resulting in four deaths.

It isn’t clear whether the Seattle Genetics drug caused the deaths or liver damage. The FDA imposed the holds on the trials to evaluate the potential risk of hepatotoxicity in patients who were treated with the drug, the company said.

The patients had taken the experimental drug either before or after undergoing stem-cell transplants. A stem-cell transplant is a common treatment for leukemia, and involves taking blood or bone-marrow stem cells from a healthy donor and infusing them into the patient after the patient undergoes high-dose radiation or chemotherapy.

Rachel Lerman of the Seattle Times reports that the drugs target specific cells and dump toxins into certain cells to fight cancer:

The company is investigating whether the drug being tested is related to the deaths.

“Seattle Genetics is working diligently 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 company said in a news release.

The affected patients had received stem-cell transplants either before or since starting treatment. Six patients have been diagnosed with liver damage, known as hepatotoxicity, including four who died.

More than 300 patients have been treated with the drug.

Seattle Genetics specializes in developing antibody-drug conjugates, or ADCs.

The drugs target specific cells and dump toxins into certain cells to fight cancer.

Juliet Preston of MedCity News writes that one analyst urged investors not to overreact:

Shares were down 14.6 percent in premarket trading, but Needham & Company Analyst Chad Messer urged investors not to overreact:

“The hold stems from concerns for potential liver toxicity in patients that receive stem cell transplants before or after treatment. While we expect shares to trade down this morning, we caution investors not to overreact as liver toxicity is a known side effect of stem cell transplantation.”

Four clinical trials are underway for vadastuximab in AML. Three of these are geared towards newly-diagnosed patients and have reported low toxicity.

But something went horribly wrong in the fourth trial, which aimed to treat relapsed AML in a mixed group of pre- or post-transplant patients. It is unclear at this point whether the adverse events were caused or worsened by Seattle Genetics’ therapy.