Abstract :
The management of patients with differentiated thyroid cancer involves scanning with radioiodine (I-131). Current practice requires withdrawal of thyroid hormone (TH) for several weeks to raise endogenous TSH to levels sufficiently high to stimulate uptake in thyroid remnant and/or metastases. During the period of withdrawal patients develop hypothyroid symptoms which may sometimes be debilitating.
Recombinant human TSH (rhTSH, Genzyme) has been tested in two multicenter clinical trials. In the first trial (Meier et al, J.Clin.Endocriol.Metab 78: 188, 1994), rhTSH was injected i.m. for either 1, 2, or 3 days while TH (L-T3) was continued. Patients after recent thyroidectomy (N=19) were given I-131 24 hr after the last dose of rhTSH and 48-hr whole-body scans were done. Then L-T3 was stopped for 20 days, and a second I-131 dose was given to obtain “withdrawal” scans, so that patients served as their own controls. I-131 uptake by thyroid remnants (normalized to body background) and scan results after rhTSH were similar to those in the hypothyroid phase. This initial trial, which included patients with uptake inside (N=19) and outside the thyroid bed (N=3), indicated that rhTSH can be safe and effective in raising serum TSH to levels sufficiently high to allow both radioiodine scanning and serum thyroglobulin (Tg) measurement without the need to withdraw TH.
The second trial of rhTSH, recently completed, provided useful information on 127 patients, including 15 patients with local and distant metastases (Ladenson et al, manuscript submitted). The protocol was similar to that of the first trial. Scans were read by a panel of independent reviewers. The quality and diagnostic yield of the scans performed with rhTSH were usually equal or better than the conventional “withdrawal” scans, and the patients felt much better after rhTSH (while euthyroid) than during the hypothyroid phase. Few ontoward effects of the rhTSH injections were noted: transient, usually mild nausea occurred infrequently. Serum Tg levels at 48-96 hr rose as often after rhTSH as after TH withdrawal. A third study is currently in progress, targeting additional patients with local and distant metastases, which is designed to confirm the safety and efficacy of rhTSH for diagnostic scanning and Tg testing.
Overall the clinical experience with rhTSH to-date indicates that the agent is safe and allows both I-131 scanning and serum Tg measurements while patients remain on TH therapy. Future studies will be needed to assess the role of rhTSH in I-131 therapy.
