S&P Dow Jones Indices announced late Thursday it was booting Nektar Therapeutics NKTR, -2.32% from the S&P 500 index SPX, +1.59% . Nektar was the worst performing stock on the benchmark index in the past 12 months, dropping more than 70%. Nektar's earnings per share fell 112% in the second quarter, the third worst performance among companies included in the S&P 500. Nektar is set to be replaced by Las Vegas Sands Corp. LVS, +2.28% , which gained more than 5% in the extended session Thursday. The change will take effect Oct. 3. Nektar stock was up 1.9% in after-hours trading Thursday and will move to the S&P MidCap 400. This is the third announced change to the S&P 500 in the past two weeks. Previously, S&P Dow Jones Indices announced that NVR Inc. NVR, +0.55% and CDW Corp. CDW, +2.09% would join the benchmark S&P 500.