By Jess Jones Pharma giantGSK is in hot water as it faces a barrage of lawsuits over its heartburn drug Zantac, which tens of thousands allege has caused them to develop cancer. A US court ruling on Friday has significantly increased the stakes for the company, after a judge ruled that scientific evidence presented by lawyers in more than 70,000 cases was valid. GSK and the other drugmakers involved, Pfizer and Sanofi, dispute the claims that Zantac causes cancer and GSK has said it plans to appeal the Delaware ruling. Following this decision, the London-listed firm’s shares plunged almost 10 …