At a time when much of the biopharma space can’t seem to get enough of antibody-drug conjugates (ADC), Bristol Myers Squibb Co. is backing away from a potential $3 billion-plus collaboration with Eisai Co. Ltd., handing back full rights to the latter’s folate receptor alpha-targeting ADC, farletuzumab ecteribulin (FZEC), citing a portfolio reprioritization.