Apple CEO Steve Jobs poses with the new iPhone 4 during the Apple Worldwide Developers Conference in San Francisco, California in this June 7, 2010 file photo. [Photo/Agencies]

Apple's future

Gleacher & Co analyst Brian Marshall said investors would undoubtedly question Apple's long-term momentum, given Jobs' outsized role in developing the company's hit products.

"Clearly Steve is a visionary. And at $350 a share this is going to weigh on investors," he said.

Richard Windsor, global technology specialist at Nomura, agreed that Jobs' absence should not have a fundamental effect, but added: "Perception of the company is another matter."

"Steve Jobs is seen by the market to be a major force in Apple's strategic direction. If his pancreatic cancer has returned, one could be quite worried."

Apple has been notoriously close-mouthed about Jobs' medical condition. He had surgery in 2004 for an unusual type of tumor on his pancreas called a neuroendocrine tumor - which often is not quite as deadly as pancreatic cancer. The tumors can cause hormone imbalances, like the one that prompted Jobs to take medical leave in 2009.

Jobs had a liver transplant in 2009, and organ transplant recipients sometimes have recurring health issues for life, in part because they often must take immune-suppressing drugs to prevent organ rejection.

Jobs was noticeably thin following his transplant surgery in 2009, and he still appeared so at recent Apple events, something that did not go unnoticed.

But the CEO said last summer he was feeling "great," in response to a question from a reporter.

Apple is due to report quarterly results on Tuesday, and is expected to say that revenues rose 50 percent as sales of its iPad tablet computer grew on momentum of the popular iPhone and earlier iPod.