Apple Chief Executive Steve Jobs broke with his usual code of secrecy Monday to explain his health problems, but the disclosure that a hormone imbalance was causing his noticeable weight loss will probably do little to tamp down concerns.

Medical experts said a hormone imbalance in a pancreatic cancer survivor raises red flags about a possible recurrence. Jobs said in 2004 that he had undergone surgery to treat a rare form of the deadly disease.

Although Jobs is known as one of the nation's most intensely private corporate leaders, he issued an open letter Monday in which he tried to assure Apple investors and customers that he was healthy enough to lead the pioneering technology company he co-founded.

The 53-year-old CEO said his doctors discovered his condition had been "robbing" his body of proteins needed for good nutrition. He is undergoing treatment, which he described as simple and straightforward.

He did not mention cancer in his letter.

"I've said more than I wanted to say, and all that I am going to say, about this," Jobs wrote.

Several medical experts, who had no access to Jobs' health records, said problems other than cancer could have caused a hormone imbalance. For example, the surgery to remove his tumor could have left Jobs with a pancreas too small to produce the necessary enzymes.

Yet hormone imbalances are common in people who have an active neuroendocrine tumor, not in people who have been cured of the cancer, said Dr. Selwyn M. Vickers, chairman of the surgery department at the University of Minnesota.

An Apple spokesman declined to comment. The board said it would give Jobs its "complete and unwavering support" while he recovered.

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-- Dawn C. Chmielewski and Jessica Guynn

Photo credit: Associated Press