Steve Jobs, Apple's chief executive, is likely to be suffering from a recurrent cancer tumour of the pancreas or complications relating to his earlier surgery to deal with the disease, doctors said today.

Speculation is rife about the cause of the "hormone imbalance" that he says is forcing him to take a leave of absence from his role as head of the iconic technology firm.

But doctors said today that, given the length of time Mr Jobs is planning to take off, and his own opaque description of symptoms, persistent rumours that he has experienced a recurrence of cancer or could be facing surgery to remove his pancreas were the simplest explanations for his illness.

Rumours began last summer when Apple's army of followers on the internet remarked upon Jobs's dramatic weight loss as he launched of a new version of the iPhone, with some noting that Mr Jobs had surgery for pancreatic cancer in 2004 and that at the time Apple had been cagey about his condition.

The newswire service Bloomberg unwittingly kept the issue in focus by accidentally publishing an obituary of Mr Jobs in August. Then two months later a contributor to a news blogging site owned by CNN, iReport, wrongly reported that Jobs had suffered a "major heart attack", sending Apple's shares down 11 per cent within 10 minutes.

Mr Jobs said earlier this month that his condition was "robbing me of the proteins my body needs to be healthy".

Richard Ross, a professor of endocrinology at the Royal Hallamshire Hospital in Sheffield, said that a hormone imbalance could be a result of his earlier surgery.

"Pancreatic cancers are typically extremely aggressive and people die fairly often from them, but there are less common types of tumour, known as carcinoid tumours, which are more benign and run a benign course.

"My suspicion, based on the limited information we have, is that Mr Jobs had, or currently has, a benign tumour of the pancreas and is suffering problems related to that.

"Treatment is usually an operation to remove the tumour but, depending on how much of his pancreas or small bowel he had removed, he may be deficient in enzymes which regulate the digestion of protein and fats.

"Alternatively, he may be deficient in insulin, which is also produced by the pancreas and would require him to take regular insulin injections."

A common imbalance of this type is diabetes. If so, this news is not necessarily devastating and the treatment could still be "simple and straightforward", as Mr Jobs has suggested.

Both diagnoses would be consistent with dramatic weight loss and could be treated either with nutritional supplements mixed in with food or insulin, Professor Ross said.

Martyn Lobley, a GP and Times columnist, agreed that that anyone who has lived for four years after being treated for pancreatic cancer is both lucky and likely to have been cured of the disease.

However, Dr Lobley added that the vague and simplistic language used by Mr Jobs to describe his condition does not really reveal much at all.

For example, the idea that he is losing "proteins" may mean that he has a bowel condition unconnected to his previous surgery or cancer.

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