A rare form of pancreatic cancer that has afflicted Apple Inc CEO Steve Jobs responded so well to Pfizer Inc's drug, Sutent, that a study was stopped early so all patients could take the pill.

An independent safety board monitoring the late-stage study recommended halting it after concluding that Sutent delayed progression of the cancer compared with people taking a placebo along with standard treatment, Pfizer said on Thursday.

Patients who took Sutent in the trial will be allowed to continue doing so, and those who were given placebos will now have the option of taking the drug.

Patients in the study had advanced pancreatic islet cell tumors, also known as neuroendocrine cancer. It occurs in specialized cells of the pancreas that secrete a variety of hormones, including insulin and enzymes involved in digestion.

Other types of pancreatic cancer occur in ducts of the pancreas — small tubes that transport digestive enzymes produced in the pancreas to the small intestine.

"This form of pancreatic cancer involves only about 5 percent of all pancreatic cancer cases, and grows and spreads more slowly" than other types of pancreatic cancer, said Mace Rothenberg, a senior Pfizer research executive.

When surgery to remove the cancer is not possible, or when cancer returns after surgery, Rothenberg said life expectancy is only several years, and patients can experience difficult symptoms, such as life-threatening high levels of insulin and stomach ulcers.

Sutent is currently approved for treating advanced kidney cancer as well as gastrointestinal tract tumors.

Jobs Had Surgery

Jobs, who co-founded Apple Computer and turned it into a consumer juggernaut after returning as chief executive a decade ago, underwent surgery in 2004 to remove an islet cell tumor from his pancreas.

In January, Jobs said he would take a five-month medical leave because his health problems were more complex than originally thought.

The tech innovator acknowledged that he had been losing weight throughout 2008 and said his doctors determined a hormone imbalance had been depriving him of vital proteins. That triggered speculation that his cancer had returned and was upsetting hormones involved in digestion.

Blockbuster in the Making

Sutent, which had fourth-quarter sales of $220 million, is also undergoing late-stage studies against cancers of the breast, lungs, colon, prostate and liver.

Herman Saftlas, an analyst with Standard & Poor's, predicted on Thursday that Sutent would generate annual sales of $1.5 billion by 2013, up from his earlier view of $1.4 billion.

"Pfizer has had a lackluster history of drug development, but got some good news today," said Saftlas, adding that the trial results bolstered company shares in an already strong rally for the broad stock market.

Pfizer's stock was up 9.7 percent to $14.03 in afternoon trading, outpacing a 4.6 percent rise in the American Stock Exchange Pharmaceutical Index of large U.S. and European drugmakers.