The biggest upside surprise from the American Society for Clinical Oncology meeting in Chicago, which ends Tuesday, probably came from , a beleaguered biotech that came back to life thanks to its antibody drug conjugate mirvetuximab soravtansine, or IMGN853. The drug's objective response rate - the percentage of tumors that shrank - was 53%, which induced several price-target increases and an upgrade to equal weight from Morgan Stanley.