OncoMed's offering of 4.8 million shares priced at $17 per share. It had expected a pricing range of between $14 and $16 a share.
Company shares, which are listed on the Nasdaq Global Select Market under the ticker symbol "OMED," spiked 56 percent, or $9.70, to $26.70 in morning trading.
OncoMed is based in Redwood City, Calif., and it is studying therapies that target cancer stem cells, the cells that cause growth and metastasis of tumors. OncoMed has five drugs in clinical testing.
The underwriters of the IPO will have the option to buy another 720,000 shares to cover over-allotments.