Skip to main content

Main menu

  • Home
  • Content
    • Current issue
    • Past issues
    • Early releases
    • Collections
    • Sections
    • Blog
    • Infographics & illustrations
    • Podcasts
    • COVID-19 Articles
    • Obituary notices
  • Authors & Reviewers
    • Overview for authors
    • Submission guidelines
    • Submit a manuscript
    • Forms
    • Editorial process
    • Editorial policies
    • Peer review process
    • Publication fees
    • Reprint requests
    • Open access
    • Patient engagement
  • Members & Subscribers
    • Benefits for CMA Members
    • CPD Credits for Members
    • Subscribe to CMAJ Print
    • Subscription Prices
    • Obituary notices
  • Alerts
    • Email alerts
    • RSS
  • JAMC
    • À propos
    • Numéro en cours
    • Archives
    • Sections
    • Abonnement
    • Alertes
    • Trousse média 2023
    • Avis de décès
  • CMAJ JOURNALS
    • CMAJ Open
    • CJS
    • JAMC
    • JPN

User menu

Search

  • Advanced search
CMAJ
  • CMAJ JOURNALS
    • CMAJ Open
    • CJS
    • JAMC
    • JPN
CMAJ

Advanced Search

  • Home
  • Content
    • Current issue
    • Past issues
    • Early releases
    • Collections
    • Sections
    • Blog
    • Infographics & illustrations
    • Podcasts
    • COVID-19 Articles
    • Obituary notices
  • Authors & Reviewers
    • Overview for authors
    • Submission guidelines
    • Submit a manuscript
    • Forms
    • Editorial process
    • Editorial policies
    • Peer review process
    • Publication fees
    • Reprint requests
    • Open access
    • Patient engagement
  • Members & Subscribers
    • Benefits for CMA Members
    • CPD Credits for Members
    • Subscribe to CMAJ Print
    • Subscription Prices
    • Obituary notices
  • Alerts
    • Email alerts
    • RSS
  • JAMC
    • À propos
    • Numéro en cours
    • Archives
    • Sections
    • Abonnement
    • Alertes
    • Trousse média 2023
    • Avis de décès
  • Visit CMAJ on Facebook
  • Follow CMAJ on Twitter
  • Follow CMAJ on Pinterest
  • Follow CMAJ on Youtube
  • Follow CMAJ on Instagram
Commentary

Explaining the increasing incidence of differentiated thyroid cancer

Jacques How and Roger Tabah
CMAJ November 20, 2007 177 (11) 1383-1384; DOI: https://doi.org/10.1503/cmaj.071464
Jacques How MB ChB
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Roger Tabah MD
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • Article
  • Responses
  • Metrics
  • PDF
Loading
  • © 2007 Canadian Medical Association or its licensors

The thyroid is the largest of the endocrine glands and by far the most common site of all primary endocrine cancers. However, thyroid cancer is relatively rare, accounting for only 1% of all cancers. The number of new cases diagnosed each year is comparable to that of leukemia, pancreatic cancer and oropharyngeal cancer.1 Published in this issue of CMAJ are the results of a study in which Kent and colleagues2 used the Ontario Cancer Registry to identify 7422 cases of differentiated thyroid cancer from 1990 to 2001. Their results show that the incidence of this type of thyroid cancer increased by 146% over the 12-year study period, for an overall increase of 13% per year. Similar findings have been reported lately in many countries, including the United States.3 Earlier studies included one by Liu and colleagues,4 who studied the incidence of thyroid cancer in Canada (excluding Quebec) from 1970 to 1996 using the Canadian Cancer Registry. They reported an increasing trend: the overall age-adjusted incidence rates of thyroid cancer doubled from 3.3 per 100 000 in 1970–1972 to 6.6 per 100 000 in 1994–1996 among female patients, and from 1.1 per 100 000 to 2.2 per 100 000 among male patients in the same time frame. There is a remarkable and impressive congruency among these worldwide reports, which identified that the increased incidence occurred almost exclusively with papillary thyroid carcinoma, particularly the microlesions (< 1 cm).

Given the unequivocal evidence that the incidence of papillary thyroid carcinoma has increased over the past number of decades, the obvious question is why. One explanation is that we may be witnessing a true increase in the incidence of thyroid cancer, which has been termed “an epidemic of micropapillary thyroid cancers.” A second is that the rising number of cases is apparent only because of changes in medical practice, particularly the increased use of ultrasonography and fine-needle aspiration biopsy. Alternatively, the reason for the increased incidence may be a combination of both of these explanations. The answer will be fundamentally important, since an understanding of the basic causes and related risk factors — especially previously unrecognized ones — for thyroid cancer may lead to novel therapeutic interventions and preventive measures.

Similar to previous studies,3,5 Kent and colleagues conclude from their Ontario data, that the increased incidence of thyroid cancer is due to increased detection of small, subclinical tumours through the use of medical imaging. Davies and Welch3 attributed this apparent increase to the phenomenon of “increased diagnostic scrutiny.” However, these studies lack clinical data, such as the proportion of patients in each tumour-size group who underwent neck imaging and fine-needle aspiration biopsy, and the proportion of patients with incidentally detected thyroid cancer. Nevertheless, there is consensus to support their conclusions.

Studies in France for the period 1980–2000 have correlated the increased incidence of thyroid cancer with the increased use of ultrasonography (from 3% to 84% of patients) and cytological procedures (from 8% to 36% of patients).6 More recently, Burgess and Tucker7 provided evidence that, in Tasmania, increasing use of preoperative fine-needle aspiration biopsy led to an increase in the incidence of papillary thyroid carcinoma, especially tumours 1 cm or smaller. They also observed an increase in the incidence of tumours larger than 1 cm in patients without a history of preoperative fine-needle aspiration biopsy, which suggests that the occurrence of clinically relevant tumours has increased. Interestingly, Kent and colleagues found that the incidence of medium-sized tumours (2–4 cm) remained stable over time, but were surprised to discover a slight increase in large tumours (> 4 cm) among patients 45 years and younger.

These findings are surprising since modern imaging should help diagnose clinical lesions earlier. However, the opportunity and need for neck imaging for both thyroid disorders and nonthyroid indications vary for different age groups and for men and women. Moreover, if medical imaging and fine-needle aspiration biopsy are the only factors facilitating the recognition of an increasing number of micropapillary thyroid carcinomas, why is it that other thyroid cancer histotypes, such as follicular and medullary carcinomas, do not follow a similar trend? Admittedly, nonpapillary thyroid cancers occur much less frequently than papillary thyroid cancers. Perhaps even more important is the fact that a large number of undiagnosed, clinically occult cases of papillary thyroid carcinoma exist in the community, as deduced from autopsy studies that revealed a rate of 2.7%–36% of such cancers.2 Indeed, in an informative and often-quoted autopsy study by Harach and colleagues8 reported that close to 36% of individuals who had thyroid cancer that was undiagnosed during their lifetimes harboured 1 or more foci of thyroid cancer.

Seeking theoretical support for their findings and interpretation, Kent and colleagues allude to the increasing number and use of computed tomography and magnetic resonance imaging scanners in Canada, which should further inflate the number of incidentally detected cases of thyroid cancer. Paradoxically, there is a concern that the radiation exposure incurred through computed tomography scanning will increase the risk of cancer. In a provocative but thoughtful editorial, Baker and Bhatti9 recently suggested that the rapid increase in computed tomography use could, at least in part, account for the increasing incidence of thyroid cancer. In addition, they offered a plausible explanation as to why the thyroid may be at particular risk: iodine, which is trapped by the thyroid gland, blocks photons more readily, so that the radiant energy that reaches the thyroid is more apt to be deposited locally instead of passing through. The situation is exacerbated following the intravenous administration of iodine-contrast media, and such increased energy deposition can cause DNA breaks that lead to mutations.9

Irrespective of the precise causes of the increasing incidence of papillary thyroid carcinoma, particularly microlesions, we are faced with therapeutic dilemmas about how to manage the ever-increasing number of patients presenting with malignant thyroid microlesions. The majority of micropapillary thyroid cancers have very good long-term prognoses, but some do give rise to metastases and require more aggressive treatment. Unfortunately, we currently do not have reliable means to predict which of these tumours will be harmless and which will become troublesome. Kent and colleagues argue that the management of these small thyroid tumours may be based on an outdated model culminating in unnecessary investigations and overly aggressive surgery. This conclusion echoes that of Davies and Welch,3 who emphasized the risks of “overdiagnosis” and, in addition, made the bold, but highly controversial, statement that papillary thyroid cancers smaller than 1 cm could be classified as a normal finding. We would find it hard, if not impossible, to use such an approach in our office when confronted with a patient who has a cytologically proven micropapillary thyroid carcinoma. In an accompanying editorial to the paper by Davies and Welch, Mazzaferri10 made a plea that we should not be too complacent with regard to the management of small papillary thyroid carcinoma. Papillary thyroid carcinoma is highly heterogeneous, and despite similar histological appearances, its biology and clinical behaviour can vary remarkably from one patient to another. The discovery and development of specific and sensitive markers, especially molecular and genetic, is urgently needed to facilitate the understanding of the basic biology and allow a clinically meaningful risk stratification of each subgroup and variant of papillary thyroid carcinoma. We agree with the philosophy of Colonna and colleagues5 that we need to find a compromise between overdiagnosis and beneficial early screening.

@ See related article page 1357

Potential explanations for the increasing incidence of papillary thyroid carcinoma

• Increased incidence of small, subclinical papillary thyroid carcinoma

• Changes in medical practice such as increased use of neck imaging and fine-needle aspiration biopsy

• Greater exposure to radiation associated with increased use of computed tomography scanning

Footnotes

  • Contributors: Both authors worked on all aspects of the manuscript, including its design, data analysis and interpretation. Both authors drafted and revised the manuscript and approved the final version.

    Competing interests: None declared.

REFERENCES

  1. 1.↵
    Tuttle RM, Leboeuf R, Martorella AJ. Papillary thyroid cancer: monitoring and therapy. Endocrinol Metab Clin North Am 2007;36:753-78.
    OpenUrlCrossRefPubMed
  2. 2.↵
    Kent WDT, Hall SF, Isotalo PA, et al. Increased incidence of differentiated thyroid cancer and detection of subclinical disease. CMAJ 2007;177:1357-61.
    OpenUrlAbstract/FREE Full Text
  3. 3.↵
    Davies L, Welch HG. Increasing incidence of thyroid cancer in the United States, 1973–2002. JAMA 2006;295:2164-7.
    OpenUrlCrossRefPubMed
  4. 4.↵
    Liu S, Semenciw R, Ugnat AM, et al. Increasing thyroid cancer incidence in Canada, 1970–1996: time trends and age–period–cohort effects. Br J Cancer 2001;85:1335-9.
    OpenUrlCrossRefPubMed
  5. 5.↵
    Colonna M, Guizard AV, Schvartz C, et al. A time trend analysis of papillary and follicular cancers as a function of tumour size: a study of data from six cancer registries in France (1983–2000). Eur J Cancer 2007;43:891-900.
    OpenUrlCrossRefPubMed
  6. 6.↵
    Leenhardt L, Grosclaude P, Chérié-Challine L. Increased incidence of thyroid carcinoma in France: A true epidemic or thyroid nodule management effects? Report from the French Thyroid Cancer Committee. Thyroid 2004;12:1056-60.
    OpenUrl
  7. 7.↵
    Burgess JR, Tucker P. Incidence trends for papillary thyroid carcinoma and their correlation with thyroid surgery and thyroid fine-needle aspirate cytology. Thyroid 2006;16:47-53.
    OpenUrlCrossRefPubMed
  8. 8.↵
    Harach HR, Franssila KO, Wasenius VM. Occult papillary carcinoma of the thyroid: a “normal” finding in Finland. Cancer 1985;56:531-8.
    OpenUrlCrossRefPubMed
  9. 9.↵
    Baker SR, Bhatti W. The thyroid cancer epidemic: Is it the dark side of the CT revolution? Eur J Radiol 2006;60:67-9.
    OpenUrlCrossRefPubMed
  10. 10.↵
    Mazzaferri EL. Managing small thyroid cancers. JAMA 2006;295:2179-82.
    OpenUrlCrossRefPubMed
PreviousNext
Back to top

In this issue

Canadian Medical Association Journal: 177 (11)
CMAJ
Vol. 177, Issue 11
20 Nov 2007
  • Table of Contents
  • Index by author

Article tools

Respond to this article
Print
Download PDF
Article Alerts
To sign up for email alerts or to access your current email alerts, enter your email address below:
Email Article

Thank you for your interest in spreading the word on CMAJ.

NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

Enter multiple addresses on separate lines or separate them with commas.
Explaining the increasing incidence of differentiated thyroid cancer
(Your Name) has sent you a message from CMAJ
(Your Name) thought you would like to see the CMAJ web site.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Citation Tools
Explaining the increasing incidence of differentiated thyroid cancer
Jacques How, Roger Tabah
CMAJ Nov 2007, 177 (11) 1383-1384; DOI: 10.1503/cmaj.071464

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
‍ Request Permissions
Share
Explaining the increasing incidence of differentiated thyroid cancer
Jacques How, Roger Tabah
CMAJ Nov 2007, 177 (11) 1383-1384; DOI: 10.1503/cmaj.071464
Digg logo Reddit logo Twitter logo Facebook logo Google logo Mendeley logo
  • Tweet Widget
  • Facebook Like

Jump to section

  • Article
    • Footnotes
    • REFERENCES
  • Responses
  • Metrics
  • PDF

Related Articles

  • Highlights of this issue
  • Dans ce numéro
  • Increased incidence of differentiated thyroid carcinoma and detection of subclinical disease
  • PubMed
  • Google Scholar

Cited By...

  • Are thyroid nodules associated with sex-related hormones? A cross-sectional SPECT-China study
  • Do US thyroid cancer incidence rates increase with socioeconomic status among people with health insurance? An observational study using SEER population-based data
  • The influence of the environment on the development of thyroid tumors: a new appraisal
  • Thyroid Cancer Incidence among Active Duty U.S. Military Personnel, 1990-2004
  • Incidental thyroid "PETomas": clinical significance and novel description of the self-resolving variant of focal FDG-PET thyroid uptake
  • Evaluation of the thyroid nodule
  • Rising Thyroid Cancer Incidence in the United States by Demographic and Tumor Characteristics, 1980-2005
  • Google Scholar

More in this TOC Section

  • Ensuring timely genetic diagnosis in adults
  • The case for improving the detection and treatment of obstructive sleep apnea following stroke
  • Laser devices for vaginal rejuvenation: effectiveness, regulation and marketing
Show more Commentary

Similar Articles

Collections

  • Topics
    • Cancer & oncology
    • Endocrinology

 

View Latest Classified Ads

Content

  • Current issue
  • Past issues
  • Collections
  • Sections
  • Blog
  • Podcasts
  • Alerts
  • RSS
  • Early releases

Information for

  • Advertisers
  • Authors
  • Reviewers
  • CMA Members
  • CPD credits
  • Media
  • Reprint requests
  • Subscribers

About

  • General Information
  • Journal staff
  • Editorial Board
  • Advisory Panels
  • Governance Council
  • Journal Oversight
  • Careers
  • Contact
  • Copyright and Permissions
  • Accessibiity
  • CMA Civility Standards
CMAJ Group

Copyright 2023, CMA Impact Inc. or its licensors. All rights reserved. ISSN 1488-2329 (e) 0820-3946 (p)

All editorial matter in CMAJ represents the opinions of the authors and not necessarily those of the Canadian Medical Association or its subsidiaries.

To receive any of these resources in an accessible format, please contact us at CMAJ Group, 500-1410 Blair Towers Place, Ottawa ON, K1J 9B9; p: 1-888-855-2555; e: cmajgroup@cmaj.ca

Powered by HighWire