By Bethany Wales Delaware’s top court is set to hear an appeal from GSK and other pharmaceutical giants to throw out over 70,000 lawsuits alleging that the now-discontinued heartburn drug Zantac caused cancer. The companies, which also include Pfizer and Sanofi, are challenging a lower court ruling that allowed expert testimony claiming Zantac causes cancer – a link they say is not credible. First approved by US regulators in 1983, Zantac had become the world’s best-selling drug less than five years after hitting the market, surpassing $1bn in sales. The drug, sold by four major companies, now…