"During the past week I have learned that my health-related issues are more complex than I originally thought," he wrote. Apple's chief operating officer, Tim Cook, will take over Jobs' responsibilities while he is on leave.
After-hours trading on Apple shares was halted. The Cupertino, Calif.-based company's stock had sank $2.38, or 2.7 percent, to close at $85.33.
Jobs announced in 2004 that he had undergone successful surgery to treat a very rare form of pancreatic cancer - an islet cell neuroendocrine tumor. The cancer is easily cured if diagnosed early. Jobs did not have a deadlier and more common form of pancreatic cancer called adenocarcinoma.