The Nasdaq settled above its 6,000 milestone for the first time ever and scored a new record close by the end of the session. The Dow Jones Industrial Average and S&P 500 also enjoyed big gains, their best back-to-back increases of the year. Dow component McDonald's  (MCD - Get Report) was among those contributing to the index's gains. Comparable sales increased 1.7% in the U.S. over its recent quarter as its all-day breakfast offerings continued to fuel traffic. Railroad company CSX  (CSX - Get Report) climbed this afternoon after new CEO Hunter Harrison disclosed a $15 million purchase of shares. Harrison was named CEO just last month. Express Scripts  (ESRX) slumped as it prepared investors for the loss of its largest client Anthem (ANTM - Get Report) . Anthem had sued Express in the past, claiming overcharging. Express says its contract likely won't be renewed past 2019.