Check out the companies making headlines after the bell:
Equifax shares rose more than 1 percent in extended trading. Earlier Thursday, the company announced it might have faced another cyberbreach, but the company later said that it was not hacked.
Spark Therapeutics's stock rose more than 5 percent after hours. An FDA advisory panel voted in favor of the company's gene therapy for a rare form of blindness.
Shares of Pacific Gas and Electric climbed more than 7 percent in extended trading before leveling out to nearly flat, after the stock closed down 6.7 percent during the regular session.
Baxter shares fell less than 1 percent in the extended session after the company said it expects to see an impact from Hurricane Maria on its fourth-quarter revenue.