OncoMed Pharmaceuticals Inc said it halted patient enrollment and dosing in all ongoing early-stage trials of two of its experimental cancer drugs over concerns of bone damage.
OncoMed shares fell as much as 25 percent on Friday.
The company said it halted the studies as a "precautionary measure", after reports of the drugs, vantictumab and OMP-54F28, causing mild-to-moderate bone-related side effects. Both drugs are undergoing early-stage testing as single agents in patients with advanced solid tumors, and are part of a collaboration between OncoMed and Bayer AG.
OncoMed said it would propose lower and less frequent dosing for studies of the drugs in combination with other drugs.
The company also proposed further revisions, including bone protection strategies and modified enrollment criteria, but these will need approval from both the FDA and study site institutional review boards before the enrollment and dosing of new patients can resume.
Piper Jaffrey analyst Edward Tenthoff said he did not see the two drugs as growth drivers for the stock and assigned greater value to the company's other experimental drugs, demcizumab and OMP-59R5, which are currently being tested for use in lung and pancreatic cancer.
"OncoMed is acting prudently and will not necessarily discontinue the programs that are partnered with Bayer," Tenthoff said, after trimming his price target on the stock to $43 from $48.
OncoMed also said it would continue dosing patients from completed trials who have remained on either treatment as a single agent for an extended period of time without the cancer progressing or significant drug-related side effects.
The company has various anti-cancer drugs in its pipeline and is developing antibodies and other agents that target biological pathways critical to tumor-initiating cells, also known as "cancer stem cells".
The Redwood City, California-based company's shares were trading down 15 percent at $21.17 on the Nasdaq on Friday.
(Editing by Don Sebastian and Simon Jennings)