Cancer deaths have been on pace to outnumber deaths from heart disease in the United States for some years now — but once again, in new data from the Centers for Disease Control and Prevention, they didn’t.

Heart disease has ticked upward in deaths since 2010, and it remains the number one killer of Americans.

Over the last three decades, the US has seen rising mortality from cancer and falling mortality for heart disease. Those lines had been projected to cross in recent years.“We actually thought that it would happen in 2011, but then heart disease nosed back up,” said Bob Anderson, a statistician in the CDC’s National Center for Health Statistics and a coauthor of the new report published on Wednesday.

In 2014, heart disease was responsible for 614,348 deaths while cancer was the cause of 591,699 deaths.

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The phenomenon owes to a number of possible factors, said Anderson. But demographics is one.

“Each year there are more older folks, who have a higher risk of mortality from all causes,” he said, “and a higher risk of cancer.”

Anderson also pointed to other factors, including smoking and its links to lung cancer, which currently claims more lives than any other cancer. But there have also been increases in liver cancer, he said.

“That probably has something to do with the fact that hepatitis C rates kind of went crazy in recent years,” Anderson said. “With drug and alcohol use, you can get cirrhosis of the liver, which can also become cancer.”

Anderson said that it’s unclear why deaths from heart disease have started ticking upward again. The “last two flu seasons have been kind of rough, and the flu can kill heart patients a lot sooner than they would have died otherwise,” he said. “But it could also be just random. It’s really too complicated to draw any definitive conclusion.”

And in subgroups within the US population, cancer is already the top killer. Cancer has overtaken heart disease as the leading cause of death in 22 states, as of 2014. And among Hispanic and Asian or Pacific Islander populations, cancer is the number one killer.

Nonetheless, the CDC is not likely to change its public awareness efforts any time soon.

“Many of the things we say to people — reduce tobacco use, exercise, early detection — really overlap both cancer and heart disease,” said CDC spokesperson Richard Quartarone. “So we’ll probably stay with what we’re doing.”