Antibody-drug conjugates (ADCs) are making a comeback. After a relatively slow start with Adcetris (brentuximab vedotin, Seattle Genetics Inc.) and Kadcyla (ado-trastuzumab emtansine, Roche Holding AG) approved by the FDA in 2011 and 2013, respectively, the regulatory activity has swelled with four FDA approvals over the last nine months.