You likely know the statistic: Iowa has the second-highest cancer rate in the country. It’s a data point that has come up, for example, amid the state’s ongoing fight for improved water quality. But what, exactly, does it mean that Iowa ranks second in the nation in this undesirable statistic? What goes into the data, and who puts it together?
That last question is easy: the Iowa Cancer Registry and the National Cancer Institute, part of the National Institutes of Health.
For the rest, let’s take a closer look at the statistics behind Iowa’s ignominious position near the top of the nation’s cancer rates.
Iowa’s cancer rate second and rising
In the five-year period between 2017 and 2021 — the most recent data available from the National Cancer Institute — Iowa recorded an average of 19,623 new cancer cases annually. That’s a little more than 600 new cases per 100,000 residents, based on Iowa’s population at the 2020 census, or about 0.6%.
However, it’s not as easy as saying that the average person in Iowa has a 0.6% chance to develop cancer in any given year. The odds of developing cancer vary significantly from person to person based on various risk factors, including, notably, age.
Iowa’s population has a larger share of seniors (people age 65 or older) than the U.S. as a whole. To account for this, the National Cancer Institute adjusts states’ cancer rates for the ages of their population. This is the age-adjusted cancer rate, and it’s the metric by which Iowa ranks second.
Only Kentucky (513.7 new cases per 100,000 residents) has a higher age-adjusted cancer rate than Iowa (491.8).
However, Kentucky’s cancer rate is falling, or at least stable — and Iowa’s is rising.
The National Cancer Institute estimates, with 95% confidence, that Iowa’s new cancer rate is increasing by between 0.3% and 1.2%. The only other state with a rising cancer rate is Utah, ranked 42nd in the U.S. in age-adjusted new cases per 100,000.
What cancers are contributing most to Iowa’s high rate?
Not every form of cancer is as prevalent in the state as the number-two ranking would suggest. Iowa’s age-adjusted rate of new stomach cancer cases, for example, is third-lowest among the 50 states and D.C., and more than 25% below the national average.
Iowa also has a below-average rate of liver and bile duct cancer, as well as ovarian cancer. But each of those types of cancer is already relatively rare, and among more common types, Iowa fares worse.
Iowa has about 5% and 11% more new cases of breast and prostate cancer, respectively, than the national average.
Those are two of the most common cancer types, with an age-adjusted rate of more than 125 new cases apiece per 100,000 Iowans. The National Cancer Institute data shows those rates are rising within the state, too.
Other common cancers also occur at a greater rate in Iowa than the rest of the U.S., including lung cancer (15% more prevalent than the national average), colorectal cancer (10%), uterine cancer (9%) and melanoma or skin cancer (38%).
Who has been most at-risk for developing cancer in Iowa?
Older people have a higher risk of developing cancer, and that’s been particularly true in Iowa. The state’s new cancer rates among the population 50 and older and the population 65 and older each rank second in the nation. The rates of new cancers for those age groups in Iowa are both more than 10% higher than the national rate, and both are on the rise.
If there’s a small bright spot among the data, it may be that Iowa’s cancer rates are lower than the national average on the other end of the age spectrum: the rate of new cases among Iowa children under 20 is about 3% lower than in the rest of the country.
Other demographic data provided by the National Cancer Institute is less encouraging.
Both men and women in Iowa develop cancer at rates about 10% higher than the rest of the country. The state ranks fourth and third, respectively, in age-adjusted new cancer rate for men and women.
There’s a similar story for race and ethnicity demographics, particularly among Iowa’s Black and indigenous populations, which each have new cancer rates more than 20% higher in Iowa than the rest of the country.
Geographically, there is no clearly identifiable trend in the distribution of new cancer cases across Iowa.
Four rural counties in different parts of the state — Palo Alto, Cass, Cherokee and Appanoose — have the highest age-adjusted cancer rates, according to National Cancer Institute data.
Polk County, the state’s largest and home to Des Moines, sits in the middle of the pack. Its neighbors, Dallas and Story (among the state’s youngest), have new cancer rates among the lowest dozen of Iowa’s 99 counties.
Tim Webber is a data visualization specialist for the Register. Reach him at twebber@registermedia.com and on Twitter at @HelloTimWebber.
This article originally appeared on Des Moines Register: Iowa has the second-highest cancer rate in the US. What exactly does that mean?
Reporting by Tim Webber, Des Moines Register / Des Moines Register
USA TODAY Network via Reuters Connect
