Mayo Clinic researchers are reporting new hope in the fight against a form of pancreatic cancer that doctors thought to be inoperable — and terminal within 18 months.

Survival rates from pancreatic cancer have been poor, in part because surgery has been considered futile when tumors have spread beyond the organ itself. But Mayo this week reported three features that predicted better outcomes for patients with “locally advanced” cancers, those that hadn’t reached other organs but had spread beyond the pancreas to attached blood vessels.

“The goal is to extend patients’ lives and maintain or improve their quality of life,” said Dr. Mark Truty, an oncologic surgeon at Mayo in Rochester.

Pancreatic cancer is the eighth-most common form in the United States, but the fourth-leading cause of cancer death. Roughly one third of the 55,000 pancreatic cancers diagnosed each year in the U.S. are found at the locally advanced stage.

Studying the results of 194 patients with cancers at this stage, Mayo researchers found that survival was longer in those who received extended chemotherapy before tumor-removal surgery. Average survival was even longer if blood work showed that the chemotherapy had reduced a key protein to normal levels before surgery, and it was longer still if the tumors removed during surgery were found to already have been killed by the chemotherapy.

These discoveries are significant, because advances in chemotherapy and surgery make it possible to focus treatment plans around these three predictors of survival, Truty said. “We can take all of these advances and put them together to get the outcomes we are looking for.”

Results of the study, published Tuesday in the Annals of Surgery, showed average survival of nearly five years for patients who had two of the three markers.

The research followed patients over seven years and couldn’t set an average survival length for patients with all three markers because more than half were still alive at the end of the study period. Eleven percent of the patients had none of the three markers; their average length of survival was less than two years.