Section of Cancer Surveillance, International Agency for Research on Cancer, Lyon, France.
Knowledge and Evaluation Research Unit in Endocrinology, Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic, Rochester, Minnesota, USA.
Thyroid. 2020 Jun;30(6):838-846. doi: 10.1089/thy.2019.0684. Epub 2020 Mar 2.
Thyroid cancer (TC) incidence rates have been increasing in many countries, predominantly due to overdiagnosis. It is, however, not yet clear whether a true increase in exposure to risk factors might have also contributed to the TC epidemic. We assessed the TC mortality trends, which should not be affected by overdiagnosis, to disentangle the specific contribution of period and cohort effects. We analyzed long-term mortality data in 24 countries from 5 continents using age-period-cohort (APC) models. Nonidentifiability of the APC models was circumvented by integrating evidence of a consistent relationship between age and TC mortality, allowing to estimate period and cohort linear effects. Substantial heterogeneity existed in the historical TC mortality rates across countries, but long-term rates declined over time in most of the countries, converging around a value of 0.5/100,000. The shape of the age-specific curves was consistently similar across countries and periods, resembling straight lines on the log-log scale, with the slopes ranging between 4.0 and 6.0. Both period and cohort effects showed long-term declines in most countries for both genders. In some countries, such as the United States, Canada, and Australia, substantial long-term declines by period were visible until the 1980s and 1990s, but then stabilized or increased slightly. Declining cohort effects were also seen in almost all countries, and were particularly pronounced in women from Switzerland, whereas stable cohort effects were recorded in South Africa. Although there were some indications of possible increasing risks of deaths among the youngest generations in some countries for both men and women, changes are too recent to be treated as unequivocal and estimates suffered from large statistical variability due to small numbers of deaths. Global long-term declines in TC mortality have been accompanied by downward trends in both period and cohort effects. Our results suggest lack of evidence of a possible major contribution of "real" risk factors in TC mortality, and indirectly confirm the main role of overdiagnosis in the epidemic of TC incidence.
甲状腺癌（TC）的发病率在许多国家都呈上升趋势，主要是由于过度诊断。然而，目前尚不清楚危险因素的真实暴露是否也促成了 TC 流行。我们评估了不应受过度诊断影响的 TC 死亡率趋势，以厘清时期和队列效应的具体贡献。我们使用年龄-时期-队列（APC）模型分析了来自 5 大洲 24 个国家的长期死亡率数据。通过整合年龄与 TC 死亡率之间存在一致关系的证据，规避了 APC 模型的不可识别性，从而可以估计时期和队列的线性效应。各国之间的历史 TC 死亡率存在很大的异质性，但大多数国家的长期死亡率随时间呈下降趋势，最终收敛到 0.5/100,000 左右。不同国家和时期的年龄特异性曲线形状基本相似，在对数-对数尺度上呈直线状，斜率范围在 4.0 到 6.0 之间。在大多数国家，两性的时期和队列效应都显示出长期下降。在一些国家，如美国、加拿大和澳大利亚，直到 20 世纪 80 年代和 90 年代，都可以看到明显的长期时期下降，但随后趋于稳定或略有上升。几乎所有国家都出现了下降的队列效应，在瑞士女性中尤为明显，而南非则记录了稳定的队列效应。尽管一些国家的男性和女性的最年轻几代人中存在死亡风险增加的迹象，但变化发生得还不够久远，不能被视为明确的趋势，而且由于死亡人数较少，估计值受到很大的统计变异性的影响。全球 TC 死亡率的长期下降伴随着时期和队列效应的下降趋势。我们的结果表明，缺乏 TC 死亡率的“真实”危险因素可能有重大贡献的证据，间接地证实了过度诊断在 TC 发病率流行中的主要作用。
