Steve Jobs's Health: History and Speculation

On Monday, Steve Jobs announced he was taking a medical leave of absence from Apple Inc. It's the latest chapter in the visionary CEO's tale of health woes, a story that began in 2004.

In August of that year, Jobs announced, via an internal memo, that he was taking one month off to recover from surgery to treat his recently diagnosed pancreatic cancer. A pancreatic-cancer diagnosis usually results in a swift and brutal death—Patrick Swayze was diagnosed in early 2008, and died in September 2009, beating the odds by lasting that long. But while most pancreatic cancer affects the exocrine glands, Jobs's tumor was on the endocrine glands, a variation that accounts for about 1 percent of all pancreatic cancers. In these cases, the cancerous cells, while still difficult to treat, are slower-moving. The median prognosis for this type of variation is five to seven years, though the cancer can be eliminated completely if it's operated on fast enough.

Jobs assured his staffers the cancer had been caught early and surgery performed soon after, but apparently that wasn't soon enough. His rapid weight loss in 2008 was initially written off by Jobs as an easily treatable hormone imbalance—but nine days later, he announced he'd be taking a six-month leave of absence from Apple due to health issues that were "more complex than I initially thought." (Jobs also noted that the constant rumors about his health were "a distraction not only for me and my family, but everyone else at Apple as well.")

In late June, the same month he was supposed to return to work, The Wall Street Journal reported that Jobs received a liver transplant a few months prior.

The liver lies directly beneath the pancreas and receives that organ's drainage, so it's the next to suffer as pancreatic cancer spreads. The liver purifies the body's bloodstream—including preventing any cancerous cells from spreading to the lungs and the rest of the body—making it more essential to daily function than the pancreas. Replacing the liver removes the cancerous liver cells (though those in the pancreas remain), and provides a fresh line of defense against cancer spreading to the bloodstream.

At the time of Jobs's transplant, 15,771 Americans were waiting for a donor liver, and his ascension to the top of the list had ethicists concerned that he'd used his wealth to improve his odds. According to ABC News, doctors suspected Jobs used a practice they call multiple listings, in which a patient is evaluated at several transplant centers and, if deemed a worthy candidate, put on the list at all those locations. Due to insurance restrictions, most patients are able to be evaluated at only one center—and wouldn't have the means to quickly travel to distant centers should organs became available there.

After the transplant, Jobs mostly made headlines just for his products, not his prognosis. Now, however, the speculation about his health—and his longevity as CEO—has resumed.

It could be that Jobs's body is rejecting his new liver. Though most rejection happens soon after the transplant, living with a donated organ means a lifetime of mitigating the body's instinct to fight it.

Another possibility is grimmer: that the cancer has destroyed this new liver, making it unable to perform its normal functions and increasing the odds that the cancer will spread to the lungs. From that point, the cancer could theoretically spread to the rest of the body, though doctors note that most patients don't live long enough for that to happen.

There is also a chance, of course, that Jobs has thrown out his back, or needs a particularly invasive series of root canals, or wants to attend an immersive six-month-long vegan cleansing retreat. At this point, Jobs, his doctors, and Apple are silent on the specific health issues that have required him to abandon his post. But given his health history—and the traditionally troublesome outcome of patients with any kind of pancreatic cancer—there's a good reason people are worried.

This article orginally appeared on The Daily Beast.