Nektar plummets on lower-than-expected response rates

Nektar Therapeutics (NASDAQ:NKTR) fell $37.78 (42%) to $52.57 Monday after the company said it will start Phase III testing of its NKTR-214 plus anti-PD-1 mAb Opdivo nivolumab based on lower-than-expected Phase I/II response rates reported Saturday at the American Society of Clinical Oncology meeting in Chicago. The stock move implied skepticism that substantially lower response rates among patients enrolled in the second of the trial's two stages would rise over time.

At ASCO, Nektar and partner Bristol-Myers Squibb Co. (NYSE:BMY) reported updated data from cohorts of patients with first-line stage IV melanoma, renal cell carcinoma (RCC) and urothelial carcinoma in the Phase Ib/II PIVOT-02 trial...