U.S. stocks were down slightly on Thursday as the S&P 500 maintains its longest losing streak since the financial crisis in 2008. The healthcare sector fell the most at 1.10%.

Two of the most active players, Teva Pharmaceutical Industries(TEVA) - Get Report and Pfizer(PFE) - Get Report , drove down the sector. Shares of Teva Pharmaceutical Industries fell almost 10% to $39.20 after Bloomberg reported that the Israel-based company has received subpoenas for its suspected role in price collusion with other generic pharmaceutical companies.

New York-based drug-maker Pfizer reported worse-than-expected third-quarter profit of 61 cents a share on Tuesday. It also announced a surprising end to the late-stage development of an experimental cholesterol-lowering drug. Shares of Pfizer decreased 2.42% to $29.89 today.

The Dow Jones Industrial Average lost 29 points, or 0.16%, down to 17,930. The S&P 500 index fell 9 points, or 0.44%, to 2,088, and the Nasdaq composite declined about 47 points, or 0.92%, to 5,058.

The biggest losers of the day were Achillion Pharmaceuticals(ACHN) - Get ReportPacific Biosciences of California(PACB) - Get ReportImpax Laboratories (IPXL) Akorn(AKRX) - Get Report and Insmed(INSM) - Get Report

New Haven, CT.-based biopharmaceutical company Achillion Pharmaceuticals reported a net loss of $20.7 million, or 15 cents per share, compared with net income of $26.3 million (19 per share) for the third quarter of 2015 in its third quarter earnings release today. Shares of Achillion tumbled almost 29% to $4.32 by the closing bell.

Menlo Park, CA.-based genetic-sequencing company Pacific Biosciences of California announced its third quarter earnings after the market closed on Wednesday. The company reported revenue totaled $25.1 million, up 80% compared to $13.9 million for the third quarter of 2015. Despite that, shares Pacific Biosciences of California dipped almost 20% to $6.65 per share at the market's close. 

Shares of Hayward, CA.-based Impax Laboratories Inc fell almost 20% to $16.50. The specialty pharmaceutical company is set to release its third quarter earnings on Nov. 9.

Akorn, another specialty pharmaceutical company, saw its shares drop about 18% to $20.27 despite reporting a net revenue of $284 million for the third quarter 2016, an 11% increase year-over-year. 

Shareholder rights law firm Robbins Arroyo recently took a class action complaint was filed against Akorn for alleged violations of the Sherman Antitrust Act and the Clayton Antitrust Act by Akorn's officers and directors. A press release from the law firm accused Akorn of price collusion with its competitors that caused certain drug prices to spike nearly 700%.

Bridgewater, NJ.-based biopharmaceutical company Insmed shares fell almost 14% to $10.36 after posting third quarter 2016 today. The company reported a net loss of $37.8 million, or $0.61 per share, compared with a net loss of $31.0 million, or $0.50 per share, for the third quarter of 2015.