North Carolina health officials say they will study an unusual number of thyroid cancer cases that have been detected in Iredell County and, in greater numbers, two ZIP codes of southern Iredell.
The county health director requested an assessment by the N.C. Central Cancer Registry in March because five-year rates of the cancer were higher than those in the rest of the state.
The cancer registry, in a May 29 report, found that most of the cases came from two ZIP codes, 28115 and 28117. Both are in the area of Mooresville and eastern Lake Norman.
"Based on the (ratio) analyses, the number of thyroid cancers in Iredell County and the two zip codes were statistically greater than expected," the report states. It cautions that the assessment can't be used to identify the cause of the cancers or links to risk factors that might have caused it.
About 54,000 new cases of thyroid cancer are diagnosed each year, the American Cancer Society says, with 75 percent of those cases in women in their 40s or 50s. About 2,060 people a year die from the disease.
The report is "more validation and that’s what we need," former cancer patient Jennifer Brown told WBTV.
Brown was 39 when she was diagnosed in January. Now cancer-free after treatment, she's part of a study by a Duke University scientist into thyroid cancer in the area.
The cancer registry compared the number of observed cancer cases with the number of cases that would be expected in the state. It looked at cases reported during 22-year (1995-2016) and five-year (2012-16) time periods.
For the longer period, 475 cases were reported in Iredell County, about 50 percent more than would be expected. The number of cases in the two ZIP codes were even higher — the 260 total cases were more than double the expected number.
The gap between observed and expected cases further increased between 2012 and 2016, with cancer cases in the 28117 ZIP code nearly three times higher than expected.
The cancer registry report will be sent to the Occupational and Environmental Epidemiology Branch of the N.C. Department of Health and Human Services for further study. The report acknowledges several limitations in it, such as not including people who once lived in the county or the two ZIP codes but lived elsewhere when they were diagnosed.
The Division of Public Health is helping local health departments better understand the occurrence of thyroid cancer in the area and gather information about potential exposures, DHHS spokeswoman Cobey Culton said.
The department says it will review cancer registry data to understand who's developing cancers, review medical literature for potential environmental links and assess the feasibility of gathering more information on the reported cases.
"Information gathered during next steps will help inform whether a study can be done to look for a common exposure or risk factor among thyroid cancer cases in this area of North Carolina," Culton said by email.
Along with gender, inherited conditions and family history, a diet low in iodine and exposure to radiation are risk factors in developing the disease, the American Cancer Society says. Radiation sources may range from medical treatments that included radiation treatments or power plant accidents, it says. Duke Energy's McGuire nuclear plant on Lake Norman is south of the two ZIP codes being studied.
Despite the Iredell County numbers, it's rare for researchers to prove that cancer cases constitute a statistical "cluster."
Just south of Iredell County, the town of Huntersville is using a $100,000 state grant to look for answers to an unusual number of cases of a rare eye cancer called ocular melanoma. While only about five new cases per 1 million people are diagnosed, nearly two dozen cases have been reported in the town of about 56,000 in recent years.
A year-long analysis of environmental clues, reported in April, came up empty even as a similarly large number of cases were reported among people who had studied or worked at Alabama's Auburn University.