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Americans in certain struggling parts of the country are dying from cancer at rising rates, even as the cancer death rate nationwide continues to fall, an exhaustive new analysis has found.

In parts of the country that are relatively poor, and have higher rates of obesity and smoking, cancer death rates rose nearly 50 percent, while wealthier pockets of the country saw death rates fall by nearly half.

Prostate cancer ultrasound BSIP / UIG via Getty Images

Better screening and treatment have contributed to the improvement in the nation as a whole — but the study underscores that not all Americans have benefited from these advances.

"We are going in the wrong direction," said Ali Mokdad, the study's lead author and a professor at the University of Washington's Institute for Health Metrics and Evaluation. "We should be going forward, not backward."

"We all know this is unacceptable ... in a country that spends more than anybody else on health."

Stark differences in regional cancer death rates have been found in previous research, but this one stands out for providing detailed estimates for deaths from nearly 30 types of cancer in all 3,100 U.S. counties over 35 years.

Related: Cancer Deaths Fall 25 Percent

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From 1980 to 2014, the U.S. death rate per 100,000 people for all cancers combined dropped from about 240 to 192 — a 20 percent decline. More than 19 million Americans died from cancer during that time, the study found.

The picture was rosiest the Colorado ski country, where cancer deaths per 100,000 residents dropped by almost half, from 130 in 1980 to just 70 in 2014; and bleakest in some eastern Kentucky counties, where they soared by up to 45 percent.

"We all know this is unacceptable ... in a country that spends more than anybody else on health," Mokdad said.

The Affordable Care Act took effect in the study's final years and emphasized prevention services including no-cost screenings for breast, colorectal and cervical cancers. Any resulting benefits wouldn't be evident in the latest results, since cancer takes years to develop. It's unknown whether similar coverage will be part of the replacement system the Trump administration and Congressional Republicans are seeking.

Related: Cancer's the Top Killer in 21 States

An editorial published with the study by Stephanie Wheeler, a University of North Carolina health policy specialist and Dr. Ethan Basch, a University of North Carolina cancer specialist, notes that many areas with the highest cancer death rates also strongly supported Donald Trump, "raising hopes that future policies developed by the incoming administration will provide resources" for these communities.

Researchers estimated county death rates using U.S. government death records and U.S. Census Bureau data. Results were published Tuesday in the Journal of the American Medical Association. Among the more striking disparities:

In counties with the highest 2014 cancer death rates, six of the top 10 were in eastern Kentucky. Six of the 10 lowest rates were in the Colorado Rockies.

For lung cancer deaths, four of the five counties with the highest 2014 rates were in eastern Kentucky, with rates up to 80 percent higher than in 1980. Three of the five counties with the lowest 2014 rates were in the Colorado Rockies, where rates dropped by up to 60 percent.

Death rates for breast and colorectal cancers increased in Madison County, Mississippi and in 2014 were at least five times higher there than in Summit County, Colorado, where the rates fell. These are among cancers that can be successfully treated if detected early.

Related: Half of Deadly Cancers Due to Bad Habits

Smoking, obesity, physical activity and income explain many of the disparities, said study co-author Dr. Christopher Murray, also at the University of Washington.

But the study also raises questions. For example, relatively high rates of testicular cancer were found in parts of Southern California and far southern Texas for reasons that are unclear. Since treatments for this rare cancer are extremely effective, "almost nobody should die of testicular cancer," Murray said.

The poor showing for eastern Kentucky contrasts with wealthier parts of the state and "is tremendously troubling," said Ben Chandler, president of the Foundation for a Healthy Kentucky , a nonpartisan group that funds health policy research and advocacy.

Related: Obamacare Saved Thousands from Colon Cancer

Chandler cited poor access to health care and high smoking rates and said the disparities highlight a need for statewide smoke-free laws. The foundation funded a study that found that Kentucky's 2014 Medicaid expansion under the ACA covered costs for many cancer-related preventive health measures including mammograms and colon cancer screenings.

How that expanded access will fare under with the health care law's expected repeal "has been of great concern to us," Chandler said.

Ahmedin Jemal, an American Cancer Society researcher, said better understanding variations in cancer death rates will help target cancer prevention and control.