Recombinant TSH (Thyrogen®) for ablation of thyroid remnant tissue post-thyroidectomy for thyroid cancer

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Recombinant TSH (Thyrogen®) for ablation of thyroid remnant tissue post-thyroidectomy for thyroid cancer

Original article by: Yuet Wan

Source: London Cancer New Drugs Group

Date published: 11/03/2009 12:42

Summary

by: Yuet Wan

131I ablation of remnant thyroid tissue following a total or near-total thyroidectomy for thyroid cancer is carried out in the hypothyroid state to increase endogenous TSH release and thus promote uptake of radioodine into the remaining thyroid tissue. Usually thyroid replacement therapy has to be withheld from patients for 3 to 6 weeks before ablation in order to achieve an adequate TSH level. This can have a profound negative effect on the patient’s quality of life.
Recombinant TSH (rhTSH, Thyrogen®) has been developed as a source of exogenous TSH and allows patients to remain on thyroid hormone replacement therapy whilst promoting radioiodine uptake and thyroglobulin production by thyroid cells. It is licensed for use in pre-therapeutic stimulation in low risk post-thyroidectomy patients maintained on hormone suppression therapy for the ablation of thyroid remnant tissue (in combination) with 131I.
Data from a RCT (Pacini et al) showed comparable thyroid remnant ablation rates in patients prepared with rhTSH whilst on thyroxine (euthyroid group) and those in whom thyroid hormone had been withheld, but the euthyroid group was able to sustain a better quality of life and received less radiation exposure to the blood. In this study, 33 patients were randomised to the euthyroid group (received rhTSH) and 30 to the hypothyroid (control) group, who did not receive thyroid replacement therapy postoperatively. All patients with evaluable results in both groups were successfully ablated and based on criterion of no visible uptake alone, 24 of 32 euthyroid (75%) and 24 of 28 hypothyroid patients (86%) were successfully ablated (p = 0.3). Fractional uptake of radioiodine 48 hours after administration of 131I tended to be lower in the euthyroid group (p = NS) and the dose to the blood was also lower in this group (p < 0.0001). The euthyroid group improved in seven of eight physical and mental health domains between baseline and week 4 on the SF-36 scale whereas there was a decrease in quality of life in seven of eight SFF-36 domains in the hypothyroid group. Billewicz scores (degree of clinical hypothyroidism) were higher in the hypothyroid group compared with the euthyroid group at week 4 (p < 0.0001); the most common complaints in the hypothyroid group compared with the euthyroid group were cold intolerance (50% vs. 21%), weight increase (60% vs. 21%), constipation (43% vs. 3%), slow movements (50% vs. 12%), cold skin (47% vs. 12%) and periorbital puffiness (50% vs. 0%). However it is not known if there is a difference in long term outcomes between the two groups, particularly disease recurrence.
A French prospective randomised open label study has also demonstrated that rhTSH preserves the quality of life of patients undergoing radioiodine remnant ablation (RRA).
A retrospective analysis of patients followed up a median of 2.5 years after RRA found that rhTSH is associated with rates of persistent disease and clinically evident recurrence that are similar to those for traditional THW.
Guidance from the Royal College of Physicians and the British Thyroid Association describe the following situations where rhTSH is the only possible or safe option for diagnostic purposes, ablation or therapy: hypopituitarism, functional metastases causing suppression of serum TSH, severe ischaemic heart disease, previous history of psychiatric disturbance precipitated by hypothyroidism, and advanced disease/frailty.
According to the findings of a German cost effectiveness study which used data from the RCT (Pacini et al), the additional benefits of rhTSH (0.0495 QALY) are obtained with an incremental societal cost of 47 Euros, equating to an incremental cost per QALY of 958 Euros. This, the authors conclude, represents good value for money with the benefits to patient and society obtained at modest net cost. The additional costs of purchasing and administering rhTSH were largely offset by the ability to discharge the patient from the radio-protective unit earlier and more rapid return to work.
Cost of 900 mcg vial Thyrogen is £232.50; cost of treatment (2 doses) for ablation is £465.