Tumour dosimetry and response in patients with metastatic differentiated thyroid cancer using recombinant human thyrotropin before radioiodine therapy

The development of recombinant human thyrotropin (rhTSH) has given clinicians new options for diagnostic follow-up and treatment of patients with differentiated thyroid cancer (DTC). This paper evaluates the tumour dosimetry and response following -iodine-131 treatment of metastatic thyroid cancer patients after rhTSH stimulation instead of classical hormone withdrawal-induced hypothyroidism. Nineteen consecutive ¹³¹I treatments in 16 patients were performed after rhTSH stimulation. All patients had undergone a near-total thyroidectomy followed by an ablative dosage of ¹³¹I. They all suffered from metastatic or recurrent disease showing tumoral ¹³¹I uptake on previous post-treatment scintigraphy. Dosimetric calculations were performed using ¹³¹I tumour uptake measurements from post-treatment ¹³¹I scintigrams and tumour volume estimations from radiological images. Response was assessed by comparing pre-treatment serum thyroglobulin (Tg) level with the Tg level 3 months post treatment. In 18 out of 19 treatments, uptake of ¹³¹I in metastatic or recurrent lesions was seen. The median tumour radiation dose was 26.3 Gy (range 1.3–368 Gy), and the median effective half-life was 2.7 days (range 0.5–6.5 days). Eleven of 19 treatments (10/16 patients) were evaluable for response after 3 months. ¹³¹I therapy with rhTSH resulted in a biochemical partial response in 3/11 or 27% of treatments (two patients), biochemical stable disease in 2/11 or 18% of treatments and biochemical progressive disease in 6/11 or 55% of treatments. Our study showed that although tumour doses in DTC patients treated with ¹³¹I after rhTSH were highly variable, 45% of treatments led to disease stabilisation or partial remission when using rhTSH in conjunction with ¹³¹I therapy, without serious side-effects and with minimal impact on quality of life. RhTSH is therefore adequately satisfactory as an adjuvant tool in therapeutic settings and is especially suitable in advanced recurrent or metastatic DTC patients who may be intolerant to TSH stimulation by levothyroxine withdrawal.