Journal of Thyroid Disorders & Therapy
Open Access

Latent Thyroid Cancer: Diagnosis and Treatment

Stephen C Allen^{* *}Correspondence: Stephen C Allen, Department of Medicine, University of Michigan, Michigan, USA, Email:

Author info »

Description

Thyroid cancer has become more common in recent years all over the world, with South Korea having one of the highest prevalence. Over the past 30 years, the standardized incidence of thyroid cancer in France has increased more than fourfold (10,100 cases registered in metropolitan France), although thyroid cancer-related mortality has reduced. Papillary carcinomas are responsible for 89-98% of the rise in thyroid cancer incidence. Thyroid cancer has, however, remained remarkably steady, according to autopsy examinations (according to the meta-analysis by Hill based on 13,000 autopsies performed between 1949 and 2007 on patients who died with no known thyroid disease).

The Researchers found latent thyroid carcinoma in 11% of patients, which impacted both men and women equally, and the prevalence has remained stable over time. What explains the discrepancy between the rising clinical incidence and the stable histological incidence? Over diagnosis of papillary thyroid carcinoma, equating to cancer identified at an asymptomatic stage, which would never have become symptomatic all across the subject's lifetime, and lack of or very sluggish growth of the tumour, the patient expired.

The presence of latent (papillary) tumours detected unexpectedly as a result of the increasing number and improved access to various thyroid imaging procedures can explain the higher prevalence of thyroid cancer due to over diagnosis. This over diagnosis is a two-fold problem. To begin with, the patient who, instead of being in good health, is suddenly diagnosed with cancer, with all of the therapeutic (potentially ineffective surgery and 131Iodine, hormone replacement treatment), psychological, and social repercussions that implies. Over diagnosis also inflates the frequency of certain malignancies incorrectly. In France, 1300 thyroid cancers were detected in 1980, with 500 deaths, however in 2012, 8200 thyroid cancers were diagnosed, with only 400 deaths.

As a result, mortality (the number of people dying every year as a result of thyroid cancer) has remained relatively constant. As a result, survival (a dependent measure linking incidence and death) has risen dramatically, which can only be explained by two non-exclusive factors

Treatments have improved; and the incidence of cases not attributable to over diagnosis has decreased in comparison to the incidence of cases due to over diagnosis. Although therapies have improved, denying the existence and impact of over diagnosis would be a heuristic judgment error (a "black swan," according to Nassim Nicholas Taleb, a philosopher and statistician). The additional 7000 papillary tumours that would never have become symptomatic are linked with zero specific mortality, and hence do not affect mortality, would therefore constitute a very significant explanation.

Some patients with thyroid Papillary Micro Carcinoma (PMC), considered to correspond to over diagnosis (just suspected, as over diagnosis can only be verified after the patient's death), were actively monitored by Japanese authors in a recent series of studies. Over diagnosis, according to a study it is defined as cases of low-risk Papillary Micro Carcinoma diagnosed on cytology with no local or distant metastatic spread, no previously observed increase in size, no thyroid capsular rupture, no signs of high grade, no tumours less than 1 cm from the recurrent laryngeal nerve's site of entry, and finally no signs of tracheal invasion.