Pancreatic cancer is deadly—only 7% of patients survive five years after diagnosis. But giving just-diagnosed patients an inexpensive blood test can help doctors choose the treatment that is most likely to improve their chances.

The test measures CA 19-9—a tumor “biomarker” found in the blood of 90% of the population. When researchers at the Mayo Clinic analyzed data on 97,000 pancreatic cancer patients in the National Cancer Data Base, they found that having elevated levels of CA 19-9 predicted a worse outcome from therapy.

The good news: Having chemotherapy before surgery instead of the usual practice of having it afterward eliminated the elevated biomarker’s negative effect. That is, these patients did as well as patients without the elevated risk. The test is widely available and costs less than $200.