Decreasing trend in thyroid cancer incidence: a study from central Italy (2007-2019)

Due to overdiagnosis, the incidence of thyroid cancer (TC) has increased in high-income countries, including Italy. Efforts have been made to address this issue since the mid-2010s, but more information is needed about how TC incidence has changed. We aim to examine the trend in TC incidence in the Lazio Region (central Italy) and assess the impact of the 2014 Italian Consensus for the Classification and Reporting of Thyroid Cytology (ICCRTC) to identify potential changes in TC diagnosis.

To identify TC cases, we conducted a population-based study (period 2007-2019) using the data from the Lazio Region Cancer Registry (5.8 million residents). We calculated the annual age-standardized incidence rates of TC for both sexes and analyzed the impact of ICCRTC on monthly incidence rates using segmented linear regression applied to interrupted time-series (ITS).

Throughout the 13 years, there was a significant decline in TC annual incidence rates, more pronounced in females. Our results are consistent with reports from outside Europe (United States and South Korea). Following ICCRTC implementation in 2014, a step-change reduction in both sexes was revealed.

Our study indicates a significant decrease in the incidence of TC, particularly among females. The ITS analysis highlights the possible role of ICCRTC in reducing overdiagnosis. As the Lazio Region reflects the Italian population in terms of various demographic, health, and lifestyle indicators, our findings can be applicable at the national level.