Differentiated Thyroid cancer: Radioiodine Treatment

Introduction

• Radioiodine therapy:

• Has been used in the management of patients with well-differentiated (papillary or follicular) thyroid cancer since the 1940s

• Thyroid tissue has a unique ability to take up iodine from blood:

• Like iodine, radioiodine is taken up and concentrated in thyroid follicular cells:

• Because they have a membrane sodium-iodide transporter

• Compared with normal thyroid follicular cells:

• Thyroid cancer cells have reduced expression of the transporter:

• Which may account for the low iodine-131 (131-I) uptake in thyroid cancer tissue

• 131-I:

• Causes acute thyroid cell death by:

• Emission of short path-length (1 to 2 mm) beta particles

• The uptake of 131-I by thyroid tissue:

• Can be visualized by scanning to detect the gamma radiation that is also emitted by the isotope

• 131-I must be taken up by thyroid tissue to be effective:

• As a result, it is of no value in patients whose thyroid cancers do not concentrate iodide:

• Patients with medullary cancer, lymphoma, or anaplastic cancer

Goals of Radioactive Iodine Treatment

• In an effort to standardize terminology:

• An inter-societal working group with representatives from the American Thyroid Association (ATA), the European Thyroid Association, the European Association of Nuclear Medicine, and the Society of Nuclear Medicine and Molecular Imaging reached the following consensus regarding the goals of iodine-131 (131-I) therapy in differentiated thyroid cancer:

• Remnant ablation:

• The primary goal of remnant ablation is:

• Destruction of presumably benign thyroid tissue after total thyroidectomy:

• To facilitate initial staging and follow-up studies. This will, in turn:

• Improve the specificity of measurements of serum thyroglobulin (Tg) as a tumor marker

• Increase the specificity of 131-I scanning for detection of recurrent or metastatic disease:

• By eliminating uptake by residual normal tissue

• Adjuvant treatment:

• The primary goal of adjuvant treatment is destruction of subclinical tumor deposits:

• That may or may not be present after surgical resection of all known primary tumor tissue and metastatic foci

• Since adjuvant treatment is given based on the risk of having persistent / recurrent disease without definitive evidence of biochemical or structural evidence of disease:

• It is accepted that some patients selected for adjuvant treatment might already have been treated sufficiently by their primary surgery

• Thus, the decision to recommend adjuvant treatment requires:

• Balancing oncological risk (risk of persistent / recurrent disease and disease-specific mortality) and the risks associated with adjuvant treatment (short- and long-term risks of 131-I):

• With the potential benefit of adjuvant treatment (potential to decrease recurrence, improve progression-free survival, and/or improve disease-specific mortality)

• Thus, in properly selected patients, the potential benefits of 131-I adjuvant treatment could include:

• Destruction of subclinical, microscopic foci of disease remaining after surgery

• Decreased risk of recurrence

• Improved disease-specific survival

• Improved progression-free survival

• Treatment of known disease:

• The primary goal in the treatment of known disease is:

• Destruction of clinically apparent macroscopic disease (evidenced by either abnormal thyroglobulin values or structural findings) that is not amenable to surgical therapy

• Radioiodine treatment of residual disease and metastatic disease:

• May reduce the risk of recurrence and mortality:

• Especially in small-volume disease that is radioiodine avid

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