The HER2-directed antibody-drug conjugate Enhertu (trastuzumab deruxtecan) has won its fifth breakthrough therapy designation from the FDA. Enhertu was developed jointly by AstraZeneca (LON:AZN) and Daiichi Sankyo (OTCMKTS: DSNKY). The latest designation relates to treating adults with unresectable or metastatic HER2-low (IHC 1+ or IHC 2+/ISH-negative) breast cancer. Of the five breakthrough therapy designations for the drug,…