More than 75% of excess cancer cases for the top five cancers in Iowa can be explained by certain demographic and behavioral factors, according to the most recent finding from a state-funded report that seeks to better understand the state's high cancer rates.
For the past year, University of Iowa researchers looked at the state's top five cancers: prostate, breast, lung, colorectal and melanoma cancers. They make up 55% of the estimated new cancer cases this year, according to the Iowa Cancer Registry.
In a press conference on Tuesday, researchers said when they controlled for certain factors like age, race, UV exposure, alcohol and tobacco use and county radon levels, 76% of the state's excess cases could be explained.
"The results suggest that prevention efforts targeting modifiable risk factors would reduce the number of excess cases of cancer in Iowa," said Edith Parker, dean of the University of Iowa's College of Public Health.
Iowa has one of the highest rates of cancer in the country and is one of a few states where cases are increasing. Researchers aren't sure why, but the issue has grabbed the attention of state lawmakers, who approved $1 million in funding for the first year of the study, and has become a key campaign issue in the state's gubernatorial race.
The project is a collaboration between the state of Iowa and the University of Iowa. Its first year, which concluded in July, focused on demographic and behavioral risk factors. State officials said the second year will look into genetic and environmental factors and will be funded through some of the state's federal Rural Health Transformation Program allocation.
Researchers compared Iowa's cancer rates to the national average and a cluster of neighboring Midwestern states — Minnesota, Wisconsin, Nebraska, North Dakota and South Dakota — which were deemed to be the most similar to Iowa.
After comparing Iowa's cancer rates to the neighboring cluster and controlling for known risk factors, they found nearly all of the state's excess lung and melanoma cancers could be explained. Excess prostate cancer cases dropped from 280 to 118, female breast cancer cases dropped from 121 to 67 and colorectal cancer cases dropped from 118 to 37.
Unexplained excess cases in some cancers still exist in part because their causes aren't entirely known yet, said Mary Charlton, a University of Iowa professor and director of the Iowa Cancer Registry.
"Things like prostate cancer, postmenopausal breast cancer, there's some mystery left to those," she said. "We don't know either on a population basis or an individual level basis what causes all those types of cancers, but we know what some of the big risk factors are."
She said she wasn't surprised all of Iowa's excess cases for lung cancer could be explained since the causes are well-known.
The report's findings show Iowans can reduce their risk of cancer by quitting smoking, reducing the amount they drink, wearing sunblock, installing radon mitigations systems and getting cancer screenings, said Robert Kruse, the state medical director. But it doesn't fully explain Iowa's high cancer rates.
"These are population-level findings. They do not mean that questions about environmental or genetic factors have been answered. Those questions remain important, and they're important part of the work ahead," Kruse said. "But the findings do tell us that a substantial portion of Iowa's cancer burden is associated with factors where proven prevention strategies exist, and that means we should not wait to act."
