In their announcement of founder Steve Jobs’ death, at age 56, Apple officials did not mention a specific cause of death. But the visionary digital leader had been battling pancreatic cancer since 2004.
Pancreatic cancer is one of the faster spreading cancers; only about 4% of patients can expect to survive five years after their diagnosis. Each year, about 44,000 new cases are diagnosed in the U.S., and 37,000 people die of the disease.
The pancreas contains two types of glands: exocrine glands that produce enzymes that break down fats and proteins, and endocrine glands that make hormones like insulin that regulate sugar in the blood. Jobs died of tumors originating in the endocrine glands, which are among the rarer forms of pancreatic cancer.
In 2004, Jobs underwent surgery to remove the cancer from his pancreas. In 2009, after taking another leave of absence from Apple, Jobs had a liver transplant in an effort to retain as much of his organ function as possible after his cancer had spread beyond the pancreas. In January, he took a third leave from the company before resigning as CEO in August.
“I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple’s CEO, I would be the first to let you know,” Jobs wrote in a to the Apple board of directors on August 24. “Unfortunately, that day has come.”
According to experts, Jobs’ was an uphill medical battle. “He not only had cancer, he was battling the immune suppression after the liver transplant,” Dr. Timothy Donahue of the UCLA Center for Pancreatic Disease in Los Angeles, who had not treated Jobs, MSNBC.com. He noted that most patients who receive liver transplants survive about two years after the surgery.
Standard treatments for pancreatic cancer include the common tumor-fighting strategies — surgery, chemotherapy, radiation and, most recently, targeted anticancer drugs that may slightly extend patients’ lives. In 2005, the Food and Drug Administration approved , a drug that specifically targets growth factors found on cancer cells, for the treatment of patients with advanced pancreatic cancer who are receiving chemotherapy. The drug has been shown in trials to improve overall survival by 23% after a year when added to routine chemotherapy. The tumors in patients being treated with erlotinib and chemo also develop more slowly than those in patients receiving chemotherapy alone.
Because of the poor prognosis of pancreatic cancer, however, many patients elect to try alternative therapies, including a popular therapy known as the regimen, which involves fighting pancreatic tumors with pancreatic enzymes. Patients on the Gonzalez regimen also take a large number of nutritional supplements, including vitamins and minerals such as magnesium citrate, along with coffee enemas performed twice a day.
The treatment’s developer, Dr. Nicholas Gonzalez of New York, has claimed that the use of pancreatic enzymes is a powerful way to suppress the growth of advanced pancreatic cancer cells. But a study published in the Journal of Clinical Oncology in 2009, which compared groups of patients on the Gonzalez regiment to patients on standard chemotherapy treatment, found that those on chemo survived for a median of 14 months while those on the alternative therapy survived for a median of only 4.3 months.
Jobs is not reported to have tried the Gonzalez regimen, but he is known to have suscribed to alternative therapy. In a , Fortune reported that Jobs initially tried to treat his tumor with diet instead of surgery, soon after he was diagnosed in 2004. In January, Fortune that he had also made a hush-hush trip to Switzerland in 2009 for a radiation-based hormone treatment. The exact details aren’t clear, but the University Hospital of Basel in Switzerland is known for its special form of treatment for neuroendocrine cancer, which is not available in the U.S.
Whether these treatments helped to extend Jobs’ life or improve the quality of his last days isn’t clear. But cancer experts expressed surprise that Jobs survived as long as he did, continuing to fight his disease. Other pancreatic cancer patients typically aren’t as fortunate. Another high-profile patient, actor Patrick Swayze, managed to live for 20 months after his diagnosis, taking advantage of chemotherapy treatments. But, overall, patients’ median survival is generally only five months.
Jobs lost his battle with cancer at a time when researchers are constantly pushing the boundaries of treatments, particularly with antitumor agents that can home in on abnormally growing cells with increasing precision. In the end, his cancer proved too advanced to rein in with even the most innovative technologies.
“Apple has lost a visionary and creative genius, and the world has lost an amazing human being,” Tim Cook, Jobs’ successor at Apple, to employees on Wednesday. “Steve leaves behind a company that only he could have built, and his spirit will forever be the foundation of Apple.”
Alice Park is a writer at TIME. Find her on Twitter at . You can also continue the discussion on TIME’s and on Twitter at .