 Shares of Y-mAbs Therapeutics Inc. YMAB, 0.90 plunged 42.5 in premarket trading on Monday after several banks downgraded the companys stock and a Food and Drug Administration advisory committee voted against approval of the companys experimental treatment for neuroblastoma patients. The committee on Friday voted 16-0 that there wasnt enough evidence to say that omburtamab improves overall survival. 