* S&P 500 nears 2015 record high
* Oil prices hit 2016 highs
* Biogen, Alexion drop after drug trial failures
* Dow up 0.3 pct, S&P up 0.3 pct, Nasdaq down 0.04 pct (Updates to late afternoon)
By Caroline Valetkevitch
June 7 (Reuters) - The S&P 500 rose to within 15 points of its record high on Tuesday, helped by a big jump in energy shares and enthusiasm following Federal Reserve Chair Janet Yellen's speech this week.
Volume was relatively light, though, and the Nasdaq was slightly lower. Biotech shares dropped following disappointing news from several key companies including Biogen. The Nasdaq Biotech Index was down 2.2 percent.
Giving the S&P 500 its biggest boost, the S&P energy index jumped 2.3 percent and was on track for its best two-day percentage gain since March. Oil prices reached 2016 highs due to supply constraints and a weak dollar.
Gains this week have once again put the S&P 500 within striking distance of record highs reached in May 2015. Comments from Yellen on Monday seemed to ease some worries about the economy while underscoring views the Fed may be in no rush to raise rates.
"The big story for the market right now is, do we break out to all-time highs," said Michael Sheldon, chief investment officer at Northstar Wealth Partners in West Hartford, Connecticut. "If we do so in the near term, we could see a rush of money jump into the market from investors who had been sitting out on the sidelines, in fear missing out on further market gains."
At 3:18 p.m., the Dow Jones industrial average was up 48.39 points, or 0.27 percent, to 17,968.72, the S&P 500 gained 5.74 points, or 0.27 percent, to 2,115.15 and the Nasdaq Composite dropped 2.12 points, or 0.04 percent, to 4,966.59.
The Dow earlier in the day traded above 18,000, while the S&P hit its highest level since late July.
On the downside, the healthcare index dropped 0.5 percent, dragged down by Biogen and Alexion.
Biogen tumbled 12.3 percent to $254.08, and was the biggest drag on the Nasdaq and the S&P 500, after its multiple sclerosis drug failed in a mid-stage study.
Alexion dropped 10.7 percent to $138.18 after its drug failed a trial, while Valeant slumped 13 percent to $25.12 after the drugmaker cut its full-year forecast.
One of the few bright spots among biotechs was Sarepta , which surged 25 percent on hopes that its muscle-wasting treatment could yet win U.S. approval.
Advancing issues outnumbered declining ones on the NYSE by 1,930 to 1,085, for a 1.78-to-1 ratio on the upside; on the Nasdaq, 1,532 issues rose and 1,286 fell for a 1.19-to-1 ratio favoring advancers.
The S&P 500 posted 43 new 52-week highs and 1 new low; the Nasdaq recorded 80 new highs and 19 new lows. (additional reporting by Yashaswini Swamynathan in Bengaluru; Editing by Savio D'Souza)