"Wyeth must fight a two-front battle," says Elizabeth Chamblee Burch, assistant professor of law at the Florida State University College of Law. "On the one hand, it will worry about a never-ending litigation stream and have difficulty quantifying the risks. On the other hand, it will try to protect the Premarin and Prempro names." In the case of Lilly's schizophrenia drug Zyprexa, which also remains on the market, the drug's maker settled with most of the 31,300 claimants, paying $1.2 billion, and says it will fight claims by other plaintiffs, according to a recent filing with the Securities and Exchange Commission. Hormone-therapy plaintiffs could have a tougher time winning based on alleged side effects. Zyprexa plaintiffs claimed the drug caused or contributed to higher blood sugar or diabetes. Diet-drug plaintiffs alleged rare side effects such as heart-valve damage or dangerously high blood pressure in arteries of the lungs. In the hormone-therapy cases, claims involve illnesses that Wyeth's attorneys can try to attribute to many causes. "A longer latency period for cancer makes proving causation more difficult since there is an opportunity for additional intervening factors," says Burch. "There are so many different causes for breast cancer," says Thomas Metzloff, professor of law at the Duke University School of Law. "The legal system wants something where causation is clear." The most successful plaintiffs' lawsuits, he says, involve "a signature illness" such as the diseases linked to Wyeth's diet drugs or the lung-cancer mesothelioma, which has been tied to asbestos exposure.