Thyroid cancer rates on the rise across all income, education levels

Incidences of thyroid cancer increased in Denmark from 2005 to 2019 across all income and education levels, according to study findings published in Thyroid.

“Our study shows an increase in the incidence of papillary thyroid cancer and follicular thyroid cancer from 1995 to 2019 as well as small and large papillary thyroid cancers from 2005 to 2019 in Denmark,” Susanne K. Kjaer, MD, DMSc, clinical professor in the unit of virus, lifestyle and genes at the Danish Cancer Society Research Center in Copenhagen, Denmark, and colleagues wrote. “Several studies have suggested that enhanced detection may be the primary cause of the increasing rates of thyroid cancer, based on the observation that in some studies the incidence of thyroid cancer, and especially papillary micro-carcinomas, has increased more in individuals with high socioeconomic status than in individuals with low.”

Researchers analyzed data from the Danish Cancer Registry of adults diagnosed with papillary or follicular thyroid cancer from 1995 to 2019. Data on education and income level were obtained from Statistics Denmark. Adults born before 1958 with less than 7 years of education or born 1958 or later with less than 9 years of education were classified as having a short education. Those born before 1958 with 8 to 12 years of education or born from 1958 on with 10 to 12 years of education were classified as having a medium-length education. Adults with 13 or more years of education were classified as having a long education. Participants were divided into quintiles based on income levels, with the lowest quintile placed into a low income, the highest quintile placed into a high income and the remaining quintiles labeled as having medium income.

During the study period, there were 3,454 cases of papillary thyroid cancer and 972 cases of follicular thyroid cancer. The majority of thyroid cancer cases were observed in women and in adults younger than 60 years.

Papillary thyroid cancer increases in all subgroups

From 2005 to 2019, incidence rates of papillary thyroid cancer increased by an average of 12.5% annually in women with a short education, 8.1% in women with a medium-length education and 7.3% in those with a long education. Similarly, papillary thyroid cancer cases increased 13.6% in men with a short education, 9.7% in those with a medium-length education and 10.2% in men with a high education.

Papillary thyroid cancer cases increased in women with a low income by 7.4% annually, in women with a medium income by 10.2% and in women with a high income by 9.4%. Similar findings were observed for men, with an 11.6% annual increase in papillary thyroid cancer for those with a low income, an 11.8% increase in men with a medium income and a 9.7% increase in men with a high income.

Follicular thyroid cancer cases rise

Follicular thyroid cancer incidence also increased across all education and income levels. Women with a short education had a 10.5% average annual increase in follicular thyroid cancer, those with a medium-length education had a 4% increase and women with a long education had a 4.3% increase. Follicular thyroid cancer cases increased 15.5% annually in men with a short education, 7.7% in men with a medium-length education and 7.8% in those with a high education.

Cases of follicular thyroid cancer from 2005 to 2019 increased 5.9% annually in women with a low income and 7.2% in women with a medium income. There was no significant increase for women with a high income. An average annual increase in cases of 9.2% was observed in men with a low income, 10.6% in men with medium income and 8.8% in men with a high income.

The researchers speculated the increase might be due to an enhanced detection program launched in Denmark in 2007 for adults with suspected head and neck malignancies. However, they did not rule an increase in the number of cases overall, regardless of detection frequency.

“The Danish health care system provides free-of-charge health services, which may complicate comparison with studies of thyroid cancer incidence trends conducted in populations where access to health care may vary,” the researchers wrote. “Enhanced detection of thyroid cancer within the population and regardless of socioeconomic level and tumor size cannot be ruled out, but our results could also suggest that a true increase in papillary thyroid cancer and follicular thyroid cancer incidence exists.”