CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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THYROID CANCER

Abbreviations & Definitions

Recombinant human TSH-α (rhTSH) is an injectable form of thyrotropin (TSH, thyroid stimulating hormone) which is used in patients with differentiated thyroid cancer (papillary, follicular and Hürthle cell thyroid cancer). The drug has been approved for both diagnostic use and for preparing patients for radioiodine (131I) therapy to destroy any remaining thyroid tissue that persists after total or near-total thyroidectomy (remnant ablation), which facilitates follow-up and lowers recurrence rates in most patients. Studies show that the drug is therapeutically comparable to thyroid hormone withdrawal without producing symptoms of hypothyroidism (patients continue taking thyroid hormone with rhTSH). Also, rhTSH imparts 33% less whole-body radiation from 131I than occurs with thyroid hormone withdrawal.

What is the study about? This study compares the effect on tumor outcome after patients have been prepared for 131I therapy using either thyroid hormone withdrawal or rhTSH preparation.

The full article title: “Recombinant Human TSH-Assisted Radioactive Iodine Remnant Ablation Achieves Short-Term Clinical Recurrence Rates Similar to Those of Traditional Thyroid Hormone Withdrawal” It is in the Journal of Nuclear Medicine published in May 2008. (Volume 49, Issue 5, pages 764-70). The authors are RM Tuttle, M Brokhin, G Omry, AJ Martorella, SERUM Larson, RK Grewal, M Fleisher, RJ Robbins. The abstract can be obtained at:

http://www.ncbi.nlm.nih.gov/pubmed/
18413378?dopt=Citation

What is known about the problem being studied? Patients with differentiated thyroid carcinoma require high serum TSH levels before radioiodine can be given for diagnostic or therapeutic purposes. The serum TSH can be increased by stopping thyroid hormone or by injecting rhTSH. Although many studies show that rhTSH is as effective as thyroid hormone withdrawal (hypothyroidism) for preparing patients, there are no published studies comparing the clinical outcome when rhTSH or thyroid hormone withdrawal is used to prepare patients for thyroid remnant ablation.

What was the aim of the study? To compare the therapeutic effective of 131I in patients prepared with thyroid hormone withdrawal compared with rhTSH.

Who was studied? In all, 394 patients with thyroid cancer were studied; 74 underwent thyroid withdrawal and 320 were given rhTSH. Patients in the rhTSH group were significantly older than those in the withdrawal group (median age 46.5 years; range 18 to 83 vs. 44.0; range 6 to 81) but here were no other important differences in the two groups of patients and their tumors.

How was the study done? Patients were treated with 75 to 100 mCi of 131I and evaluated at 6, 12 and 18 months after surgery and 131I therapy and underwent an assessment of remnant ablation a median of 29 months after 131I therapy.

What were the results of the study? The rhTSH group was slightly but significantly more likely than the thyroid hormone withdrawal group to have no evidence of disease (76% vs. 62%,) and the rhTSH was less likely to have persistent disease than the withdrawal group ( 16% vs. 24%, P=0.1) Using slightly more rigorous criteria, patients in the rhTSH group were significantly more likely than the thyroid hormone withdrawal group to have no evidence of disease (19% vs. 32%).

How does this compare with other studies? This is the only study to compare clinical outcomes measured in terms of tumor persistence or recurrence compared with surrogate tumor markers alone such as serum thyroglobulin levels.

What are the Limitations of this study? Because this is a retrospective study, there may be patient selection bias. For instance, the older age of patients prepared with rhTSH should bias this group towards a poorer outcome, but the rhTSH group had a significantly better outcome than the thyroid hormone withdrawal group suggesting that rhTSH is even better than found in this study.

What are the implications of this study? This is the first study to clearly show that the therapeutic effect using rhTSH is at least comparable to preparing patients with thyroid hormone withdrawal.

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