The Food and Drug Administration on Wednesday approved a groundbreaking pancreatic cancer drug that experts predict will transform treatment for the notoriously deadly disease.

The drug, Revolution Medicines’ Rasonque, or daraxonrasib, was approved for patients with advanced pancreatic cancer who have already tried a prior treatment, such as chemotherapy, the agency said.

In a late-stage clinical trial of 500 patients, people who got the drug along with standard chemotherapy lived about twice as long — 13.2 months, on average — compared with people who got chemotherapy alone.

Dr. Rachna Shroff, chief of the division of hematology and oncology at the University of Arizona Cancer Center in Tucson, previously told NBC News that she “started crying tears of joy” when she saw the trial’s preliminary findings in April.

“It’s that big of a game changer for those of us who treat pancreatic cancer,” Shroff said. “It’s unprecedented.”

The drug does have side effects, including a blistering rash, sores in the mouth and throat, and vomiting and diarrhea. (Former Sen. Ben Sasse of Nebraska, who got the drug in a clinical trial, described the rash as “nuclear” on a New York Times podcast in the spring.)

Channing Der, a pharmacologist at the University of North Carolina at Chapel Hill, called Wednesday’s approval a “monumental moment for the treatment of pancreatic cancer.”

“Pancreatic cancer is the third leading cause of cancer death in the U.S. and the deadliest of all cancers,” Der wrote in an email. “This is just the beginning of more advances to come.”

Taken as a daily pill, Rasonque targets a mutation in a gene called KRAS that’s found in nearly all pancreatic cancers as well as many lung, colorectal, ovarian and other cancers. The gene acts like an on/off switch controlling how cells grow in the body. The mutation causes it to get stuck in the “on” position, spurring cells to grow out of control.

Scientists have known for years that if they could target the mutation, they could force the switch from its “on” position. But efforts have failed until Rasonque.

More than 67,000 people in the U.S. are expected to be diagnosed with pancreatic cancer this year, according to the American Cancer Society.

It’s one of the most difficult cancers to treat: There is no screening for the cancer, and early symptoms are often so vague that the majority of people are diagnosed at later stages of the disease, when it’s much more difficult to treat. The five-year survival rate for pancreatic adenocarcinoma — the most common form — is 8%.

Revolution Medicines said that more than 2,000 patients have already received Rasonque under an expanded access program that the company started in May.

The drugmaker did not say how much Rasonque would cost.