Two and a half years after FDA refused to file Genentech Inc.'s BLA for accelerated approval of Kadcyla ado-trastuzumab emtansine in metastatic breast cancer, the agency has granted full approval - and outlined its rationale behind the 2010 decision.

Drug companies still hoping to win accelerated approval in breast cancer will want to study FDA's thinking about Kadcyla. While the door is open in metastatic disease for compounds that show a robust benefit over existing treatments, developers may want to target underserved subpopulations of patients, or move upstream into the neoadjuvant setting.