US STOCKS-Wall St turns lower as Boeing, Biogen weigh

* Indexes turn lower in afternoon trading

* Broadcom (NasdaqGS: BRCM - news) and Yahoo (NasdaqGS: YHOO - news) rally after results

* Fall in crude oil weighs on energy shares

* Indexes down: Dow 0.4 pct, S&P 0.3 pct, Nasdaq 0.5 pct

By Ryan Vlastelica

NEW YORK, Oct 22 (Reuters) - U.S. stocks turned lower in afternoon trading on Wednesday, with major indexes erasing earlier gains as both Boeing (NYSE: BA - news) and Biogen sold off following their results.

Indexes had traded in positive territory for much of the session, putting the S&P 500 on track for a fifth straight day of gains. Earnings drove the move higher, with technology and material shares up on the back of strong results.

Biogen Idec (NasdaqGS: BIIB - news) was the biggest drag on the S&P 500, falling 7 percent to $303.88 after the company reported sales of its big-selling new multiple sclerosis drug, Tecfidera, that fell short of Wall Street's lofty expectations. It also reported a higher-than-expected quarterly profit and raised its full-year earnings forecast.

Boeing Co lost 3.4 percent to $122.83 despite reporting higher-than-expected earnings and lifting its outlook, as analysts raised concern about the costs of the 787 Dreamliner. Its decline comes after a rise of 5.8 percent over the four previous sessions.

Along with healthcare and industrial names, energy shares were among the day's biggest decliners, off 0.5 percent as crude oil lost 1.1 percent.

On the upside, Yahoo Inc and Broadcom rallied a day after both tech companies reported better-than-expected revenue.

Broadcom shares climbed 6 percent to $39.59 while Yahoo was up 4.4 percent at $41.96; the two made up the S&P 500's top percentage gainers.

"The season has been mixed, and the global economy is a concern for big multinational companies, but the fact that the market can shake off some bad reports is indicative of what good footing it is on right now," said Bruce Bittles, chief investment strategist at Robert W. Baird & Co in Nashville.

In the latest economic data, consumer prices rose 0.1 percent in September as energy costs fell broadly, painting a weak inflation picture that should give the Federal Reserve ample room to keep interest rates low for a while.

At 12:51 p.m. Eastern time, the Dow Jones industrial average fell 70.24 points, or 0.42 percent, to 16,544.57, the S&P 500 lost 5.63 points, or 0.29 percent, to 1,935.65 and the Nasdaq Composite dropped 21.67 points, or 0.49 percent, to 4,397.81.

Declining issues outnumbered advancing ones on the NYSE by 1,666 to 1,331, for a 1.25-to-1 ratio on the downside; on the Nasdaq, 1,699 issues fell and 904 advanced for a 1.88-to-1 ratio favoring decliners.

The benchmark S&P 500 index was posting 44 new 52-week highs and 1 new low; the Nasdaq Composite was recording 53 new highs and 20 new lows.

The S&P 500 moved 14.07 points from its session high to its session low, a move that is below the 15.6 point average over the past 250 sessions. Wednesday marks the first time the S&P has had a below-average point move since Sept. 23.

(Editing by Nick Zieminski and Chris Reese)