Moderna stock more than doubled Wednesday after the biotechnology company and Merck announced that their personalized mRNA cancer vaccine significantly delayed the return and spread of melanoma in a late-stage clinical trial. The breakthrough could give Moderna its most important commercial opportunity since COVID-19, strengthen Merck’s dominant Keytruda franchise and open the door to an entirely new class of individualized cancer treatments. However, investors should recognize that the companies have released only topline results, while detailed efficacy data, regulatory decisions, manufacturing economics and overall-survival results remain outstanding.Moderna’s long-promised second act may finally be coming into focus.Shares of Moderna jumped approximately...