Mortality rates from cancer in the United States have declined substantially during the past 3 decades, but there is still substantial regional variation in cancer-specific mortality rates across many counties, new research shows.

"Most previous reports on geographic differences in cancer mortality have focused on variation by state, with less information available at the county level," lead author Ali Mokdad, PhD, Institute for Health Metrics and Evaluation, the University of Washington, in Seattle, and colleagues report.

"And we found that cancer mortality decreased by a relative 20.1% between 1980 and 2014; however, there were substantial differences among counties through the period [and] for many cancers, there were distinct clusters of counties in different regions with especially high mortality," investigators add.

The study was published online January 24 in JAMA.

Investigators used death records from the National Center for Health Statistics (NCHS) along with population counts from the Census Bureau, the NCHS, and the Human Mortality Database to tabulate cancer deaths and population by county, among other variables.

"From 1980 to 2014, 19,511,910 cancer deaths were recorded in the United States," the authors report. Mortality rates dropped from 240.2 deaths per 100,000 population in 1980 to 192.0 per 100,000 population in 2014.

In 1980, the lowest cancer-related mortality rate, at 130.6 deaths per 100,000 population, was in Summit County, Colorado. The highest cancer-specific mortality rate was 386.9 per 100,000 population in North Slope Borough, Alaska.

In 2014, cancer-related death rates were again lowest in Summit County, Colorado. They were highest in Union County, Florida, where cancer-related death rates soared to 503.1 per 100,000 population.

Furthermore, "there were statistically significant increases in cancer mortality between 1980 and 2014 in 160 counties," Dr Mokdad and colleagues write, "with the highest rates of increase observed in Kentucky and scattered across regions of the South."

The cancer types with most deaths (a total of 5.7 million persons died between 1980 and 2014 from tracheal, bronchial, and lung cancer) showed a decline in mortality by 21% during the same period. The biggest increase from these site-specific cancers was documented in the South, the Appalachian region, and the Midwest. The biggest increase occurred in Owsley County, Kentucky, where it were it went up almost 100% between 1980 and 2014.

"Mortality from colon and rectum cancer declined by 35.5% [between 1980 and 2014]," the investigators write. Significant declines in colorectal cancer death rates were documented in most counties during the study period. In 2014, the highest death rate from colorectal cancer was again recorded in Union County, Florida, at 58.4 per 100,000, compared to the lowest rate of 8.1 per 100,000, again seen in Summit County, Colorado.

Clusters of high rates of colorectal cancer deaths were also documented along the Mississippi River in Missouri, Arkansas, and Louisiana, although such clusters were not limited to these regions alone, the investigators note.