News Track: Cancer study of Hudson neighborhood posed challenges

When about a dozen schoolteachers in Hudson were diagnosed with cancer within 10 years of each other, Diane Anderson decided to take matters into her own hands.

Anderson, who retired from teaching in the Hudson Community School District after 30 years, was one of them — diagnosed with triple negative metaplastic breast cancer, a rare form of the cancer, in 2020.

“It just really concerned me,” Anderson said. “I talked to my oncologist about it, too, and he said, for a small district — we had about 65 teachers — ‘yeah, something's wrong.’”

After her own treatment and surgery, Anderson addressed her concerns with the Black Hawk County Health Department, which referred her to the Iowa Department of Health to dig deeper into the possible cancer cluster.

However, after an investigation by the Iowa Cancer Registry at the University of Iowa ended in 2023, no conclusive cause was found in Hudson, despite a slightly elevated proportion of breast cancer in the city.

“A cancer cluster couldn't be declared, but it (was) also was not ruled out because they didn't get all of the needed information from the school that they had to have to complete it,” Anderson said. “They did the very best they could.”

After the results came back negative for a Hudson cancer cluster, Anderson reached back out the registry inquiring about breast and thyroid cancer rates in a specific neighborhood of Hudson — starting a second investigation. The results from that second investigation were released March 7.

Background

According to the American Cancer Society, a cancer cluster is defined as a “greater-than-expected number of cancer cases that occurs within a group of people in a defined geographic area over a specific period of time.” Geographic areas could include neighborhoods, towns or workplaces.

The Hudson investigations is one of the 150 cluster investigations the cancer registry has done since 1994. Only one of those investigations, however, ended with a confirmed cancer cluster — and in that case, near Wellman, researchers couldn’t find anything in the environment that appeared to be the cause.

Sarah Nash, director of research analytics and dissemination with the Iowa Cancer Registry, said the registry looks into concerns of cancer and possible clusters every time an Iowan brings them to its attention.

Nash, who also works as an assistant professor of epidemiology at UI, said the registry follows Centers for Disease Control and Prevention practices in an investigation.

She said the CDC’s process includes gathering information from the investigation’s requester, analyzing the data and sharing the findings with the requester and the Iowa Department of Health and Human Services.

What’s happened since

Nash said that when researchers are investigating a smaller area — like a specific neighborhood, which is what Anderson had requested in her follow-up — the registry doesn’t have population-level data to pull from. So researchers use a practice called a “proportional incidence ratio,” or a PIR, instead.

“It's important to note that the PIR does not tell us about risk of cancer,” Nash said. “If you think about all of the cancers in an area as a pie, it tells us that (a) slice of the pie, for example, breast cancer, is larger than the slice of the pie represented by breast cancer in the comparison area.”

Nash said using a PIR isn’t the preferred analysis since it doesn’t show the risk of cancer in the area — it shows just which cancers are more common in a certain area proportionally.

However, with more analysis, the researchers found the streets examined in the Hudson neighborhood did show a slightly elevated proportion of breast cancers in that area compared with the rest of Hudson.

But when they looked at the city compared with the rest of the state, researchers did not find an elevated standardized incidence ratio — which compares the number of observed cases of cancer in a population to the number of expected cases based on a benchmark group — for breast cancer.

“What we're trying to do here is to see, do all of these different pieces of information that we have indicate a concern?” Nash said. “We have this one piece of information which is slightly concerning, and then the other pieces of information, when we look at different time periods and analyze different areas, they're not necessarily showing us the same thing.”

Nash said it is difficult to definitively show that a cancer cluster exists but it’s even harder to prove what’s causing it. But the rates of thyroid cancer in the Hudson neighborhood jumped out to the researchers specifically, Nash said.

Despite numbers being higher, Nash said the researchers are not particularly confident in that result statistically.

The investigation’s results, which were sent to Anderson and shared with The Gazette, noted several limitations in the analysis, including using the PIR method.

“In addition, while the PIR may indicate that there is an increased risk of certain cancers, random variations in cancer cases can exist that might increase the PIR above one,” the results state. “This is especially true when comparing small populations/neighborhood areas such as this. It should also be noted that these analyses use address at time of diagnosis and do not account for any residential mobility.”

  Buy Photo

Through both investigations, Anderson has been advocating for cancer cluster research, including meeting in May with Waterloo Mayor Quentin Hart.

“Since going through treatment, I have made it my mission to help with cancer research and also created a fund for patients that cannot afford cancer care in Black Hawk County,” she said.

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Sign up here for The Gazette’s weekly environmental and outdoors newsletter.

Comments: olivia.cohen@thegazette.com