About Thyroid Cancer

Thyroid Cancer Epidemiology:

The American Cancer Society estimates that 37,340 new cases of thyroid cancer will be diagnosed in the United States in 2008.¹ Of the new cases, it is expected that approximately 28,000 will occur in women and approximately 9,000 will occur in men.¹ Although thyroid cancer generally has a good prognosis, it is estimated that in 2008, 910 women and 680 men (1,590 total) will die of thyroid cancer in the US.¹ Of all thyroid cancer deaths, 75% are due to well-differentiated (papillary or follicular) thyroid cancer.

Although the five-year survival rate for most patients with well differentiated thyroid cancer is approximately 97%, recurrences occur in approximately 30% of patients. Of all recurrences, one third may only become evident 10 or more years after initial treatment.² Given that most thyroid cancer is diagnosed in relatively young patients (20-50 years old), the routine follow-up of these patients is important.

Well-Differentiated Thyroid Cancer Risk Assessment:

There are several identified prognostic factors that may be predictive of recurrence or death in patients with well-differentiated thyroid cancer. These include patient-related factors, such as age and gender, and tumor specific factors including tumor histology, tumor size, and extrathyroidal invasion.³ Treatment related factors, such as extent of primary surgery, also influence outcome.³

The risk of recurrence and the risk of death from thyroid cancer, unlike many solid tumors, are not always concordant.⁴ Although the majority (80-85%) of patients are categorized as low risk for death from thyroid cancer,⁵ the risk of recurrence of thyroid cancer is approximately 30%. Thus, it is important to evaluate not only a patient’s risk for death from thyroid cancer, but also their risk of recurrence. As reflected in the table below, the AJCC-UICC (American Joint Committee on Cancer/ International Union Against Cancer) staging predicts risk of death.⁶

Due to the higher risk of recurrence than death from thyroid cancer, it is important to assess a patient’s risk of recurrence to determine appropriate follow-up. A three-level risk stratification has been described to characterize patients risk of recurrent disease.⁶ After the patient has undergone initial surgery and thyroid remnant ablation, the American Thyroid Association (ATA) has recommended the following risk categorization:

Low Risk: no local or distant metastases, all macroscopic tumor resected, no tumor invasion of locoregional tissues or structures, tumor does not have aggressive histology (tall cell, insular, columnar cell carcinoma) or vascular invasion, and if 131I is given, no 131I uptake outside the thyroid bed on first post treatment whole body radioiodine scan is present Intermediate Risk: microscopic invasion of tumor into the perithyroidal soft tissues at initial surgery or tumor with aggressive histology of vascular invasion High Risk: macroscopic tumor invasion, incomplete tumor resection, distant metastases, or 131I uptake outside the thyroid bed on the post-treatment scan done after thyroid remnant ablation

More information regarding risk assessment and its utility in patient management is available in the ATA 2006 Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer Guidelines

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REFERENCES:

1. American Cancer Society. Detailed Guide: Thyroid Cancer. Available at www.cancer.org accessed October 27, 2008).

2. Mazzaferri EL An overview of the management of papillary and follicular thyroid carcinoma. Thyroid 1999; 9:421–427.

3. DeGroot L, ed. Endocrinology 5^th edition. Volume 2. pg 2161-2162 2006.

4. Mazzaferri E, Kloos R. Clinical review 128: Current Approaches To Primary Therapy For Papillary And Follicular Thyroid Cancer. J Clin Endocrin Metab. 2001: 86: 1447-1463.

5. Schlumberger MJ. Papillary and follicular thyroid carcinoma. NEJM. 1998: 338: 297-306

6. Cooper D, Doherty G, Haugen B, Kloos R, Lee S, Mandel S. Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Taskforce. Thyroid 2006; 16:109-142.