Shareholder class actions are seeing an uptick after years of limping along, with two law firms out of New York leading the numbers by aggressively targeting biotech and pharmaceutical firms.

Last year's rise in investor cases—an increase of 32 percent to 44 percent, depending on the research report—was driven in large part by a surge in cases against health care, pharmaceutical and biotech companies. Lawsuits targeting life sciences firms jumped 70 percent from 2014, according to a survey provided earlier this year by Dechert. And two firms, Pomerantz & Co. and The Rosen Law Firm, filed more than half of the 67 cases in that industry.

Pomerantz is one of the oldest shareholder plaintiffs' firms in the country. The Rosen Law Firm is among the youngest. Sometimes rivals, other times partners, both firms have been consistent players in securities litigation with a relentless eye on the market of mid-tier companies.