In a pair of good news/bad news reports, the federal government said Thursday that cigarette smoking among adult Americans continues to decline sharply but that 40 percent of all cancer diagnoses now are linked to tobacco use. Those malignancies go beyond cancer in the lungs to include a dozen other parts of the body, including the throat, stomach, pancreas and liver.

Tom Frieden, director of the Centers for Disease Control and Prevention, told reporters that the latest data show how tobacco use remains “a persistent and preventable health threat” – despite smoking rates being at all-time lows. Of the 36 million current smokers, Frieden said, “nearly half could die prematurely from tobacco-related illnesses, including 6 million from cancer, unless we implement the programs that will help smokers quit.”

Between 2009 and 2013, about 660,000 people a year were diagnosed with cancers related to tobacco use, the CDC reported. About 340,000 people died of those cancers.

Yet a separate report in the agency’s Morbidity and Mortality Weekly Report shows how much progress has been made against cigarette smoking over the past decade. From 2005 to 2015, smoking among adults declined from 20.9 percent, or 45.1 million people, to 15.1 percent, or 36.5 million. The overall rate fell 1.7 percentage points last year alone, resulting in the lowest prevalence since the CDC began collecting data in 1965.

But Frieden noted that big disparities persist among different groups. Smoking rates remain higher among men, particularly black men, as well as among those who report experiencing psychological distress. People who are not high school graduates or are poor have the highest smoking rates.

“The good news is that progress is being made against smoking,” said Ernest Hawk, vice president for cancer prevention at MD Anderson Cancer Center in Houston. “The bad news is that we are leaving people behind.”

Hawk agreed with Frieden that more work needs to be done to help groups whose smoking rates remain disproportionately high and cautioned against underestimating the difficulty of quitting smoking. “Smoking is more than just a habit,” he said. “It’s an addiction, and it’s very hard to get off any addictive substance.”