San Diego biotech Halozyme Therapeutics Inc. is raising up to $115 million in a public offering of its stock, the company announced Thursday.

Halozyme plans to sell $100 million of its common stock, while offering underwriters a 30-day option to purchase up to $15 million of additional shares.

The company plans to use the money to fund the development of its cancer drug program, called PEGPH20.

Halozyme’s stock (Nasdaq: HALO) is down over 7 percent in after-hours trading Thursday. The market closed Thursday with the company’s stock selling for $14.16 per share.