A Delaware judge has ruled that GSK, Pfizer, and Sanofi must face approximately 75,000 lawsuits filed in state court regarding their former heartburn treatment, Zantac. The lawsuits allege that Zantac causes cancer, and the judge has allowed expert witnesses to testify in court. Following the ruling, GSK's shares tumbled by as much as 10% on Monday, marking their steepest decline in two years. GSK has announced plans to appeal the decision. The ruling has drawn significant media attention, and analysts suggest that GSK's potential liability could be substantial.