Overdiagnosis and overtreatment of thyroid cancer: A population-based temporal trend study

BackgroundThe increase in incidence of thyroid cancer during the last decades without concomitant rise in mortality may reflect the growing detection of indolent forms of thyroid cancer, and may have fueled unnecessary thyroidectomies. Our aim was therefore, to compare recent secular trends in surgical intervention rate for thyroid cancer with the incidence and mortality of thyroid cancer to assess overdiagnosis and resulting overtreatment.MethodsWe conducted a population-based temporal trend study in Switzerland from 1998 to 2012. All cases of invasive thyroid cancer, deaths from thyroid cancer, and cancer-related thyroidectomies were analyzed. We calculated changes in age-standardized thyroid cancer incidence rates, stratified by histologic subtype and tumor stage, thyroid cancer-specific mortality, and thyroidectomy rates.ResultsBetween 1998 and 2012, the age-standardized annual incidence of thyroid cancer increased from 5.9 to 11.7 cases/100,000 among women (annual mean absolute increase: +0.43/100,000/year) and from 2.7 to 3.9 cases/100,000 among men (+0.11/100,000/year). The increase was limited to the papillary subtype, the most indolent form of thyroid cancer. The incidence of early stages increased sharply, the incidence of advanced stages increased marginally, and the mortality from thyroid cancer decreased slightly. There was a three- to four-fold increase in the age-standardized annual thyroidectomy rate in both sexes.ConclusionsWe observed a large increase in the incidence of thyroid cancer, limited to papillary and early stage tumors, with a three- to four-fold parallel increase in thyroidectomy. The mortality slightly decreased. These findings suggest that a substantial and growing part of the detected thyroid cancers are overdiagnosed and overtreated.ImpactTargeted screening and diagnostic strategies are warranted to avoid overdetection and unnecessary treatment of thyroid cancers.

【背景】近数十年来，甲状腺癌发病率持续攀升却未伴随死亡率的同步上升，这一现象或提示惰性甲状腺癌的检出率不断提高，同时也可能催生了不必要的甲状腺切除术（thyroidectomy）。因此本研究旨在对比近期甲状腺癌外科干预率的长期趋势与甲状腺癌的发病率和死亡率，以此评估过度诊断及由此引发的过度治疗问题。

【方法】本研究于1998年至2012年在瑞士开展了一项基于人群的时间趋势研究。我们对所有侵袭性甲状腺癌病例、甲状腺癌致死病例以及与癌症相关的甲状腺切除术病例进行了分析。我们计算了按组织学亚型（histologic subtype）和肿瘤分期（tumor stage）分层的年龄标化甲状腺癌发病率（age-standardized thyroid cancer incidence rates）、甲状腺癌特异性死亡率以及甲状腺切除术率的变化情况。

【结果】1998年至2012年间，女性的年龄标化甲状腺癌年发病率从5.9例/10万人上升至11.7例/10万人（年平均绝对增幅：+0.43例/10万人/年），男性则从2.7例/10万人上升至3.9例/10万人（+0.11例/10万人/年）。发病率的上升仅局限于乳头状癌亚型——这是甲状腺癌中最惰性的亚型。早期肿瘤的发病率显著升高，晚期肿瘤的发病率仅有小幅上升，同时甲状腺癌特异性死亡率略有下降。两性的年龄标化甲状腺切除术率均上升了3至4倍。

【结论】我们观察到甲状腺癌发病率大幅上升，且这一上升仅局限于乳头状癌和早期肿瘤，同时甲状腺切除术率也同步上升了3至4倍，而甲状腺癌死亡率略有下降。上述研究结果表明，被检出的甲状腺癌中有相当比例属于过度诊断且接受了过度治疗，且这一比例正不断升高。

【研究意义】有必要采取针对性的筛查和诊断策略，以避免甲状腺癌的过度检出与不必要的治疗。