Is there really an increased incidence of thyroid cancer?

PURPOSE OF REVIEW

Between 1975 and 2009, the incidence of thyroid cancer has increased from 4.9 to 14.3 cases per 100 000 individuals, with a more pronounced increase in women (from 6.5 to 21.4 cases per 100 000 women). In the USA, in 2013, there are now more cases of thyroid cancer than all leukemias, pancreas and liver cancers combined. This review assesses the current evidence around the hypothesis that thyroid cancer is overdiagnosed: cancers are being detected that were never destined to cause a patient harm.

RECENT FINDINGS

There is a large reservoir of slow or nonprogressing thyroid cancers; up to one-third of the population may unknowingly harbor a thyroid cancer. At least two activities have contributed to the detection of this reservoir of thyroid cancer: the increasing use of advanced imaging modalities in the recent years (i.e., computed tomography and MRI) and increased rates of thyroid surgery coupled with more aggressive evaluation of excised thyroid glands. Despite the increased incidence of thyroid cancer, mortality has not changed over the last 4 decades. This mismatch between incidence and mortality is most consistent with increased identification of nonlethal disease (overdiagnosis).

SUMMARY

Thyroid cancer incidence is increasing, although mortality is stable. The major cause of the increased incidence is detection of subclinical disease - overdiagnosis. Patients are still treated aggressively and are exposed to side-effects of treatment without any certainty of benefit. Strategies to avoid unnecessary intervention and to explicitly involve patients in decision-making should be pursued. Research is needed to help predict which cancers are likely to become problematic.