Study finds no cancer clusters near CTS site

An analysis by the North Carolina Central Cancer Registry has found no evidence of cancer clusters in the immediate area surrounding the former CTS of Asheville site. But the small sample size places sharp limits on the reliability of the conclusions, researchers caution. And other types of studies being undertaken now may yield a more complete picture down the road.

The study area: The shaded circle in the center of this map shows the study area, which was within a one-mile radius of the former CTS of Asheville plant. U.S. Census data from the larger shaded area was used to estimate the population. Courtesy N.C. CCR

The three-page report, released Aug. 1, was produced in response to a request by Mountain Xpress back in early May. People living near the site had been showing up at public meetings to voice concerns about their health. Fears of cancer and other serious illnesses were rippling through conversations, and the results of an informal phone survey conducted by residents suggested that many people in the area were battling diseases. Trichloroethylene, the primary contaminant at the Mills Gap Road hazardous-waste site, is a suspected carcinogen.

To better understand the health issues, Xpress asked the Cancer Registry to analyze the existing data to see if there was an abnormally high cancer rate in the area surrounding the shuttered industrial facility. Nearly three months later, the state agency issued a report concluding: “There is no evidence of a clustering of cancer cases. Of the cancers we examined that may have a link with exposure to trichloroethylene, none appear to be present in elevated numbers.”

But that investigation is just one piece of a bigger puzzle, cautions John Masters, a health assessor who’s now working with the state Division of Public Health. Calling the study “very limited,” Masters says it “might or might not be very telling. The less samples you have, the less valid your information is going to be.” Besides the small sample size, the study was also limited because it didn’t consider the various ways that people can be exposed to the hazardous substances.

Masters, meanwhile, is conducting a more comprehensive health assessment funded by a grant from the federal Agency for Toxic Substances and Disease Registry. Although he, too, will incorporate the findings of the Cancer Registry study, Masters says he’s also using samples taken by the U.S. Environmental Protection Agency and the state Department of Environment and Natural Resources within the same one-mile radius to determine whether the actual levels of the hazardous substances pose a danger to health through the various potential exposure routes: drinking it, breathing it or touching it. The report will be based on health standards set by the Agency for Toxic Substances, which are stricter than the EPA’s standards. So far, says Masters, “I have not seen anything in the numbers that indicate something that’s immediately dangerous to life and health.”

Due out later this year, the assessment should provide a broader picture of the situation.

By the numbers

The Central Cancer Registry, an arm of the state Division of Public Health, was established in 1986. By 1990, every hospital in the state was reporting data, and the agency estimates that close to 100 percent of the state’s cancer cases now wind up in its database. In the CTS investigation, analysts focused on three types of cancer—liver cancer, renal cancer and non-Hodgkin’s lymphoma—which studies suggest may be linked to TCE exposure. Examining the area within a one-mile radius of the former industrial facility, researchers looked at the incidence of those three forms of cancer between 1990 and 2005.

To determine if the levels were abnormally high, the data was compared with expected statewide norms, which are calculated using a variety of factors, such as age, gender-specific cancer rates, and the standard incidence of each kind of cancer for the state’s population as a whole, according to statistician Seth Tyree of the Cancer Registry. The study’s methodology is also used by the Centers for Disease Control and Prevention and by cancer registries throughout North America.

Within that one-mile radius, the study found, there were 49 cases of non-Hodgkin’s lymphoma (versus 43.78 expected), 6 cases of liver cancer (versus 9.49 expected) and 4 cases of renal cancer (2.71 expected). “There were 1.12 times as many observed non-Hodgkin’s lymphoma cases, 0.63 times as many liver cancer cases, and 1.48 times as many renal cancer cases observed in the study area as expected,” the report notes, adding, “The difference between the observed and expected cases is not statistically significant. The observed number of non-Hodgkin’s lymphoma, liver cancer, and renal cancer cases all fall within the normal range [which is based on a statistical ratio].”

It may seem surprising that a total of 59 cancer cases within a one-mile radius can be considered normal. But when compared with statewide norms during that 11-year time frame, the numbers didn’t set off any alarm bells. The Cancer Registry has a very specific definition of a cluster, the report notes, and it’s not just a matter of tallying the number of cases in a given area. Analysts also look for certain clues that are associated with environmental exposure: A grouping of the same type of cancer, a group of cases among children (or with an unusual age distribution), a group of cancers that were diagnosed within a short period of time, or a clustering of rare forms of cancer. But in this case, none of those were detected.

One problem both Masters and Cancer Registry staffers were quick to point out is the very small data sample used in the analysis. “Please note,” the report states, “that the statistics for liver and renal cancers are based on a small number of observed cases, which can lead to unstable results.” The analysts chose a one-mile radius because that’s where other agencies had previously done their sampling to look for contamination, the report notes.

As CCR Director Karen Knight puts it, “These sorts of studies are fraught with problems by nature.” And sometimes, addressing one problem merely creates another one, she notes. “If we had gone out two miles, we might have diluted the results,” she explains.

In other words, the information is accurate as far as it goes, but it should be taken with a grain of salt: This isn’t the whole story.

No immediate threat detected

Masters hopes his own health assessment will provide something closer to the big picture. And though he doesn’t expect to turn in a draft to the federal agency until late September, at this point, the results look promising. “There is nothing I’ve found so far in the numbers I’ve been reviewing that constitute something that needs immediate action,” he reports.

Mills Gap Road residents first heard talk of Masters’ health assessment at a public meeting held last October. And if the final report is released this winter as projected, the whole process will have taken more than a year.

Masters concedes that it’s been slow going. “There have been several time frames set for the report to come out, but those have been pushed back based on several factors—one of them being concern from the community and questions asked,” he explains. “The report initially started out to be a consult, which is more of an abbreviated form. But after some time and more questions, it was decided that this should be an assessment—which is basically a full-blown report.

“The difference between the two is exposure pathways [i.e. inhalation, ingestion etc.]. An assessment looks at all exposure pathways. It’s meant to be an all-inclusive document that tries its best to answer any possible question that could come from the community.”

After Masters turns in his work, the federal agency will review it, and then it will be made available to the public for comments, he explains. “Then we’ll have a meeting. Once that’s done, it will be sent back in with any changes, then finalized and published.” Some Cancer Registry data will also be incorporated into the health assessment, he notes.

Grass-roots assessment inconclusive

None of the state’s efforts seem to wash with Dave Ogren, however. The neighborhood resident is a member of Concerned Citizens for a Clean and Safe Asheville, a community group that’s been pushing for a full site cleanup.

“We knew that was what they were going to come up with,” Ogren says with a sigh upon hearing the results of the cancer-cluster study. “That could have been done in 30 seconds. What we need is a boots-on-the-ground survey—an up-to-date, door-to-door survey. That would be more accurate.”

Several concerned residents took a stab at that themselves several months ago, conducting what they called a “common-knowledge health survey” by phone. As of April, their Excel spreadsheet detailed 67 known cancer cases in the area over a long period of time, winnowed from informal chats with the neighbors. The Buncombe County Health Department had considered providing equipment to support a more scientific approach, notes Ogren, but that seems to have fallen by the wayside. “I haven’t heard anymore about it,” he says, sounding frustrated. Nonetheless, Ogren says his group still plans to undertake a mass-canvassing effort in the coming months.

Marc Fowler, environmental health director for the county, says he doesn’t know of any plans for a door-to-door survey sponsored by the county. “I think there was some talk at some point that the county might be asked by ATSDR to come up with a number of individuals per household. But I think, in the end, they pursued a different avenue,” he explains. “At this point, no, we’re not going to go house to house and count heads for this thing. The primary opinion about what’s going on with respect to cancer in the area is coming from the Cancer Registry people, through ATSDR and DENR.”


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2 thoughts on “Study finds no cancer clusters near CTS site

  1. Cassandra

    Do you by chance have a link to an online version of this study? I would like to cite this study in a paper.

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