Elsevier

Clinical Oncology

Volume 22, Issue 6, August 2010, Pages 395-404
Clinical Oncology

Overview
Thyroid Cancer Epidemiology and Prognostic Variables

https://doi.org/10.1016/j.clon.2010.05.004Get rights and content

Abstract

Thyroid cancer comprises a broad spectrum of diseases with variable prognoses. Although most patients with this disease have excellent overall survival, there are some who do not fare so well. With the worldwide increase in incidence, the need to identify which tumours pose the greatest risk to patients is more acute than ever. This paper will discuss this rising trend in incidence with an analysis of the possible reasons for the increase. In addition, the paper will explore the factors that portend a worse prognosis for the individual patient. Finally, the limitations of the current staging systems will be discussed, with particular emphasis on why they are not as informative in the management of patients with thyroid cancer.

Section snippets

Statement of Search Strategies Used and Sources of Information

PubMed was searched using the keywords: differentiated thyroid cancer, TNM staging, BRAF, lymph node metastases, recurrence, mortality, radioactive iodine, incidence, radiation, and surgery. The National Cancer Institute Website was used to access the SEER monographs and the Cancer Facts and Figures Pages. Globocan was also accessed on the internet.

Incidence Rates

A study by Hundahl et al. [1] of the US National Cancer Institute’s Surveillance Epidemiology and End Results (SEER) database found 53 856 cases of thyroid cancer treated in the USA, and summarised the incidence and mortality rates of thyroid cancer from 1985 to 1995 (Table 1). This study is of considerable importance as cancers of the thyroid are relatively uncommon, comprising only 2% of all cancers diagnosed in 2009 in the USA, but involve slightly more than 95% of all cancers of the

Mortality Rates

Mortality records in the SEER database from 1973 to 2001 show relatively stable or slightly improved mortality rates for thyroid cancer per 100 000 patients [5], [9], [10]. However, over the same period, SEER mortality rates measured in terms of relative survival show an overall significant decline (P < 0.05 for trend) in mortality rates in women and an increase in mortality rates in men (P < 0.05 for trend) (Fig. 4) [5], [8].

Clinical Ramifications of Epidemiological Studies

The epidemiological features of thyroid cancer are important to clinicians for several reasons. First, PTC is the main cause of the steadily increasing incidence of thyroid cancer, mainly because it comprises about 85% of all thyroid cancers. Second, during the same period, the incidences of FTC and MTC have remained relatively stable in some studies, and the incidence of ATC has declined. Finally, perturbations of the incidence and mortality rates relate directly to decisions concerning the

Histology

Tumour histology is a critical determinant of patient outcomes; DTC is associated with the best survival rates, and MTC and ATC have significantly poorer outcomes (see Table 1) [1]. There are several histological subtypes of PTC based on the architectural features of the tumour. The most common subtype (follicular variant) has the typical cellular features of PTC with the nuclear grooves and ‘orphan Annie eye’ nuclei, but differs in that most of the tumour has a microfollicular pattern on

Conclusion

Thyroid cancer is on the rise. The reason for this increase is not clear, but it seems to be multifactorial with increased rates of detection only representing part of the equation. Numerous factors affect outcome for patients with DTC, including age, gender, tumour histology, presence of extracapsular extension, tumour size, presence of lymph node or distant metastases, and oncogene expression of the tumour. In spite of these various factors that influence the prognosis of these tumours, only

Conflict of Interest

None declared.

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