San Diego cancer drug company Halozyme Therapeutics Inc. has announced a $100 million public offering of its stock.

Shares for Halozyme (Nasdaq: HALO) dropped more than 5 percent to $13.96 in after-hours trading following the news. The company has a market cap of $1.66 billion.

The company will use the net proceeds to fund research and development of its proprietary drugs, particularly its PEGPH20 program that targets tumors of the breast, colon, pancreas and prostate.

Underwriters will have a 30-day option to purchase up to $15 million of additional shares.

The company recently appointed Onyx Pharmaceuticals Inc. veteran Helen Torley as its new CEO. Torley was previously chief commercial officer and an executive vice president at San Francisco’s Onyx, a large cancer drug company that was acquired by Los Angeles-area pharma giant Amgen in August for $10.4 billion.

Halozyme has a number of enzyme-based therapies in development, such as a drug that it’s working on in partnership with Swiss pharmaceutical company Roche Holding AG that can subcutaneously deliver a breast cancer treatment. It is also developing treatments for diabetes and dermatological conditons.

J.P. Morgan Securities LLC and Citigroup are the joint book-running managers in this deal.