The Nasdaq 100          NDX,         -2.33%        slumped 1.7% in afternoon trading Thursday, with only 17 of its components gaining ground, after the technology-friendly index ran up 3.3% over the past two days. The index’s biggest gainer was Datadog Inc. stock          DDOG,         +12.23%,        which shot up 14.3% over the monitoring and security software platform company reported before the open better-than-expected fourth-quarter results and provided an upbeat first-quarter sales outlook. Shares of Seagen Inc.          SGEN,         -11.65%        tumbled 13.8% to pace the losers after the biotechnology company reported late Wednesday a wider-than-expected loss and provided a downbeat revenue outlook. Also acting as a big drag on the Nasdaq 100 was weakness in all four of the index’s trillion-dollar-plus market capitalization companies, as shares of Apple Inc.          AAPL,         -2.34%        shed 1.7%, Microsoft Corp.          MSFT,         -2.84%        dropped 2.6%, Alphabet Inc.          GOOGL,         -2.10%        slumped 1.5% and Amazon.com Inc.          AMZN,         -1.36%        fell 1.1%.