NEW YORK - A study of Pfizer Inc's Sutent was halted early after the medicine delayed progression of a rare form of pancreatic cancer affecting tens of thousands of people globally, including Apple Inc CEO Steve Jobs.

An independent safety board monitoring the late-stage study recommended halting it after concluding that patients on Sutent stayed free of disease progression for longer than those on placebo plus best supportive care, Pfizer said on Thursday.

Given the clearly favorable trend, 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 instead.

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.

But 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, which had fourth-quarter sales of $220 million, is currently approved for treating advanced kidney cancer as well as gastrointestinal tract tumors.

Pfizer is also testing the medicine in late-stage studies against cancers of the breast, lungs, colon, prostate and liver.

Shares of Pfizer were up 5.2 percent to $13.45 in morning trading, amid a 2.9 percent rise in the American Stock Exchange Pharmaceutical Index .DRG of large U.S. and European drugmakers.

(Additional reporting by Lewis Krauskopf; editing by Gunna Dickson)