Response Genetics Inc. Chief Executive Kathleen Danenberg has resigned to focus on research and development at the company she helped found in 1999, the biotech announced Monday.

The Los Angeles developer of molecular diagnostic tests for cancer said Vice President Denise McNairn will serve as interim chief executive until a replacement is found. The board has hired executive search firm CTPartners to help identify candidates.

Danenberg will continue to have a role at the company as executive scientific and technology officer. “This transition will allow me to spend most of my time on developing new diagnostic technologies while refining our present products,” she said in a statement.

In addition to diagnostic testing, Response Genetics provides proprietary analytical testing of specimens for life science companies that are conducting clinical trials in the United States, Europe and Japan.

Danenberg’s “patented research breakthroughs have been instrumental in making RGI what it is today,” Chairman Kirk K. Calhoun said in statement. “She has established a solid scientific foundation upon which the company can continue to move forward in its development of additional diagnostic tests for cancer.”

Shares were down 23 cents, or 9 percent, to $2.67 in midday trading on the Nasdaq.