Scientists recommend expanding investigation of suspected thyroid cancer clusters in NC

North Carolina health officials should expand their investigations of suspected thyroid cancer clusters, including potential environmental causes such as coal ash, according to recommendations by a panel of doctors, scientists and medical investigators. 

The panel, many members of which are from North Carolina, convened in May and issued its report last week.

The state’s Central Cancer Registry statistics show that for the past 23 years Iredell County has reported statistically higher incidences of papillary thyroid cancer than the state average, as much as double or three times greater. In May 2018, state and county health officials designated two zip codes near Lake Norman — 28115 and 28117 — as suspected cancer clusters.

There were 260 cases of thyroid cancer diagnosed in those two zip codes from 1995 to 2016; statistically, the expected number was 124.  From 2012 to 2016, 110 cases were reported, compared to 46, the number expected.

Many of the thyroid cancer cases in Iredell County were reported among teenage girls. Although thyroid cancer rates are rising nationwide, it is still largely a disease of middle age, afflicting primarily women over 50. It is unusual for young women to develop it.

Sen. Vickie Sawyer, a Republican from Iredell County, co-sponsored Senate Bill 297, which directs the NC Policy Collaboratory to assemble a research team to help determine whether cancer clusters exist in the state, and where. The bill had bipartisan support, including several Democratic secondary sponsors, and passed both chambers. The measure was sent to the governor on July 11.

Although North Carolina as a whole ranks low among states for thyroid cancer incidences among women under 50, several counties are outliers. Elevated rates of thyroid cancer have also been reported in Rowan County, directly east of Iredell, and in five counties in southeastern North Carolina: Brunswick, New Hanover, Pender, Onslow and Duplin.

Cancer clusters are hard to pinpoint, especially in areas where people move frequently. Other environmental, lifestyle and genetic factors can also play a role in the development of cancer. The only known environmental risk factor for thyroid cancer is radiation.

Nonetheless, the panel identified ways to at least partially overcome some of those obstacles, including more detailed population studies to compare areas with elevated cancer rates and those without. These studies should also involve neighboring states to account for possible patterns in border counties.

Calculating cancer rates is dependent on accurate data. The panel said doctors should be encouraged to provide timely, consistent reporting of cancer cases to the state registry. And access to health care can also skew the results. The panel advised that future investigations should examine the role of health care access plays in cancer diagnoses.

“Areas with strong access to health care and cancer screening sometimes report higher rates of cancer than areas without such services,” the recommendations read. “Identifying areas where there are many medical practices can provide insight into how medical surveillance may contribute to thyroid cancer diagnosis.”

University scientists have already begun studying possible environmental links to the high rate of thyroid cancer in Iredell County. Heather Stapleton and Kate Hoffman, scientists at Duke University, found three homes where people had been recently diagnosed with thyroid cancer also had significantly elevated levels of compounds used in flame retardants.

Susan Wind’s teenage daughter was among the 110 people diagnosed with thyroid cancer in the affected zip codes within the last five years. Wind raised $110,000 for Stapleton’s study and has been an outspoken proponent for a detailed study of the clusters. “I believe the state should fund this research, too,” said Wind, whose family recently moved out of North Carolina because of concerns about the number of cancer cases — of several types — in their neighborhood. “It should not have to be from a private citizen whose kids got cancer. So once this study runs out of money, what is the state going to do next?”

The budget bill, still hung up over Medicaid expansion and other matters, contains no funding for studying suspected thyroid cancer clusters, though it does include $100,000 for a study of a suspected cancer cluster involving ocular melanoma in the Mecklenburg County town of Huntersville.

The panel advised the state to also investigate “potential associations” between exposure to coal ash, coal burning emissions, and papillary thyroid cancer. The two affected zip codes in Iredell County are close to Lake Norman, the site of Duke Energy’s Marshall Steam Plant. Coal ash was also widely used as structural fill throughout Iredell County.

“Given the concerns in North Carolina communities about the potential health effects of exposure to coal ash,” whose compounds can emit radiation when they decay, the recommendations read, more study is warranted. “Such studies should consider the most likely ways that people are exposed to harmful chemicals associated with coal ash: breathing them in or drinking contaminated water.”

Wind said the amount of coal ash used as fill in Iredell County was not fully documented. “It was a common practice to use coal ash like dirt, dumped in fields and sold as top soil for flower beds,” she said. “This sounds like a good hypothesis to test.”

UNC and Virginia Tech researchers recently found that more than three-quarters of 786 drinking water wells tested in Iredell County had levels of Chromium 6 above the state health advisory level of 0.07 parts per billion. Chromium 6 both occurs naturally and is present in coal ash.

Eighty-five percent of Iredell County wells had levels of vanadium, also naturally occurring and found in coal ash, above 0.3 ppb, the state’s interim maximum concentration for groundwater.

A spokeswoman for the Department of Health and Human Services said the agency “is reviewing the input from the panel and identifying the role we can play in helping to move these recommendations forward.”

[Note: This story has been updated to make clear that the proposed budget bill includes funding to study a suspected cancer cluster involving ocular melanoma in the town of Huntersville.]