BACKGROUND
The number of patients diagnosed with thyroid cancer has increased significantly in the recent decades, while death from this cancer has remained stable at a low level. This can be explained by a large number of small thyroid cancers found on different radiological tests such as ultrasound, computed tomography (CT) scanning and magnetic resonance imaging (MRI) that are done for another reason. These small cancers are mostly very low risk and may not need to be treated. Over-diagnosis is defined as finding cancer that will never cause any symptoms and will not affect the quality of life and the overall survival of a person. It has been reported that over-diagnosis accounts for up to 60-90% of all cases of thyroid cancer in different countries. Because of over-diagnosis, healthy people can undergo unnecessary diagnostic tests and treatments, including surgery, which can result in complications, in addition to experiencing the anxiety of a cancer diagnosis. Over-diagnosis is also a burden for the health-care systems because of the associated financial costs.

Over-diagnosis was thought to be correlated with the socioeconomic status such that people with a high socioeconomic status and better access to health care would be more likely to get tests leading to over-diagnosis. However, other factors may be involved, since several countries with a high socioeconomic status and access to health care, such as the Scandinavian countries and the UK, have low rates of over-diagnosis. In China, which is undergoing a rapid economic growth and urbanization, thyroid cancer is the fastest growing cancer with an average of 20% increase in diagnosis per year between 2003 and 2011. However, there are differences of up to 45-fold between the areas with low and high incidence of thyroid cancer. The aim of this study was to evaluate the factors associated with thyroid cancer over-diagnosis across different regions in China.

THE FULL ARTICLE TITLE
Li M et al 2021 Mapping over-diagnosis of thyroid cancer in China. Lancet Diabetes Endocrinol 9:330-332. PMID: 33891886.

SUMMARY OF THE STUDY
The study included data contained in 35 cancer registries from different regions in mainland China for the period 2008-2012. The study population represented 4.1% of the Chinese population, with 21 registries including patients from urban areas and 14 from rural areas. The 10 registries that also contained data between 2003-2007 were used to evaluate the change in thyroid cancer incidence over time, from 2003-2007 to 2008-2012.

A total of 27,842 patients aged 15-84 years were diagnosed with thyroid cancer (predominantly papillary thyroid cancer) between 2008-2012. The average incidence rate was 16.8 cases per 100,000 women and 5.3 cases per 100,000 men, with large variations noted across the 35 registries examined (from 0.7 to 33.9 cases per 100,000 women and from 0.4 to 11.6 cases per 100,000 men). The 21 urban registries showed a higher incidence rate (average age-standardized incidence of 19 cases per 100,000 women and 6.1 cases per 100,000 men) than the rural registries (4.9 cased per 100,000 women and 1.4 cases per 100,000 men). There was an increase of 10 and 5 cases per 100,000 women and men, respectively from 2003-2007 to 2008-2012. Similar to other countries, death from thyroid cancer has remained stable at low levels in China.

Over-diagnosis was estimated to account for 16,721 (83%) women and 4,986 (77%) men with thyroid cancer in urban registries, and for 597 (60%) women and 170 (59%) men with thyroid cancer in rural registries. Similar to other countries reporting thyroid cancer over-diagnosis, there was a change in the age at diagnostic with a peak at middle age (35-64 years) instead of older ages (65-84 years) noted in the past, this trend being more common in urban areas. Women were found to be diagnosed early in life (age 30-49 years) as compared to men, because of their more frequent use of the health system for child-bearing reasons. Thyroid cancer over-diagnosis occurred more often in regions with increased health care access. The predominant fee-for-service payment method may have contributed to over-diagnosis since it encouraged hospitals to perform more tests.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The recent increased urbanization and economic growth in China has been associated with an increase in the incidence of thyroid cancer, which can be in large part explained by over-diagnosis. These findings highlight the risk of overusing the health care system in countries undergoing economic development and the importance of implementing regulations to prevent this.

— Alina Gavrila, MD, MMSc

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