Increasing Gap Between Thyroid Cancer Incidence and Mortality in Urban Shanghai, China: An Analysis Spanning 43 Years

To examine the secular trends of thyroid cancer incidence and mortality and to estimate the proportion of thyroid cancer cases potentially attributable to overdiagnosis.

Data on thyroid cancer cases from 1973 to 2015 were obtained from the Shanghai Cancer Registry. The average annual percent change (AAPC) was evaluated using the joinpoint regression analysis. The age, period, and birth cohort effects were assessed using an age-period-cohort model. The overdiagnosis of thyroid cancer cases was estimated based on the difference between observed and expected incidences using the rates of Nordic countries as reference.

From 1973 to 2015, the number of thyroid cancer cases was 23 117, and 75% of the patients were women. The age-standardized rates were seven- to eightfold higher from 2013 to 2015 than from 1973 to 1977. Compared with relatively stable mortality, thyroid cancer incidence was dramatically increased from 2002 to 2015 in both sexes, with significant trends (men: AAPC = 21.84%, 95% CI: 18.77%-24.98%, P < .001; women: AAPC = 18.55%, 95% CI: 16.49%-20.64%, P < .001). The proportion of overdiagnosis has gradually increased over time, rising from 68% between 2003 and 2007 to more than 90% between 2013 and 2015. This increasing trend appeared to be similar between men and women.

An increasing gap between thyroid cancer incidence and mortality was observed in Shanghai, and overdiagnosis has contributed substantially to the rise of incidence, which calls for an urgent update on the practice of thyroid examination.