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After-hours buzz: GPS, AMGN, HELE & more

Gap December comps up 4%

Check out which companies are making headlines after the bell on Thursday:

Shares of Gap soared 12 percent Thursday after the bell after the retail giant reported strong holiday sales from November and December. The company saw a 2 percent increase in comparable sales overall, with a 12 percent increase at Old Navy for the month of December. Gap stores also saw a 1 percent increase in sales for the month, while Banana Republic fell 7 percent during the final month of the year. Gap's CFO, Sabrina Simmons, said the company now expects full-year earnings to come in above $1.92, which was the high end of its prior earnings range.

Amgen shares climbed 5 percent after the biopharmaceutical company won a ban on Sanofi and Regeneron Pharmaceuticals cholesterol drug, Praluent. Amgen had previously accused the two companies of infringing its patents. On Jan. 3, a a federal judge refused to throw out a court verdict that upheld Amgen's patents for Repatha. The injunction document states that Regeneron and Sanofi will have 30 days before Praluent sales are banned in order to appeal because of the public harm from removing the drug.

Helen of Troy shares climbed more than 4 percent after the bell, following its earnings report. The personal care products company reported adjusted earnings per share of $2.37, beating analysts' estimates of $1.90 a share. Its revenue of $444.4 million missed estimates of $447 million.

Helen of Troy also lowered its outlook for fiscal year 2017 primarily due to "reflect the expectation that the cough/cold/flu season will remain below average." It also cited the unfavorable currency environment as a reason for lowering its revenues to a range of between $1.52 and $1.55 billion and adjusted earnings of between $6.20 and $6.50 per share.

Shares of Shake Shack shed more than 1 percent in choppy trade Thursday after the fast casual restaurant chain named Zach Koff its first chief operating officer. Koff joined the company in 2010 and has been a member of the company's executive team since its IPO in 2015. Separately, Shake Shack also announced its CFO, Jeff Uttz, will retire, effective mid-March.

—Reuters and CNBC's Meg Tirrell contributed to this report.