Iodine excretion during stimulation with rhTSH in differentiated thyroid carcinoma

Recombinant or endogenous thyroid-stimulating hormone for radioactive iodine therapy in thyroid cancer: state of knowledge and current controversies

For patients undergoing radioiodine therapy (RIT) of differentiated thyroid carcinoma (DTC), thyroid-stimulating hormone (TSH) stimulation prior to RIT can be achieved using thyroid hormone withdrawal (THW) or administration of recombinant human TSH (rhTSH). As THW can lead to nausea, headaches, vomiting, fatigue, and dizziness secondary to transient acute hypothyroidism, rhTSH could be a good alternative. Recombinant human TSH has been administered in patients in order to stimulate TSH for RIT since 2005. According to the Martinique criteria formulated by the leading professional societies involved in care of patients with DTC, rhTSH can be applied in 3 settings: for remnant ablation, adjuvant treatment, and treatment of known disease. Numerous studies have investigated the effects of rhTSH as a method of TSH stimulation on the thyroid cell, the systemic effects, biokinetics, and clinical outcomes; however, no consensus has been reached about many aspects of its potential use. Recombinant human TSH is able to stimulate sufficient TSH levels (>30 mIU L-1) and is hypothesized to decrease risks of tumor cell proliferation. As rhTSH-use avoids the transiently impaired renal function associated with THW, radioiodine excretion is faster with the former, leading to a lower iodine-131 uptake and a difference in fractional remnant uptake, effective half-life, mean residence time, and dose to the blood. Differences between rhTSH and THW were observed in radioiodine genotoxic effects and endothelial-dependent vasodilation and inflammation. For thyroid remnant ablation, THW and rhTSH lead to similar remnant ablation rates. For adjuvant therapy and treatment of known disease, insufficient trials have been conducted and future prospective studies are recommended. The current review provides a state-of-the-science overview on the issues and debates surrounding TSH stimulation through either rhTSH adminsitration orendogenous TSH production after levothyroxin withdrawal.

Radioiodine remnant ablation in differentiated thyroid cancer after combined endogenous and exogenous TSH stimulation

Aim: Radioiodine remnant ablation (RRA) after (near-)total thyroidectomy (TE) is a key element in patients with differentiated thyroid cancer (DTC). The use of exogenous TSH stimulation (rhTSH) prior to RRA has shown promising results as compared to conventional thyroid hormone withdrawal (THW). As yet, the efficacy of RRA after brief THW and single rhTSH administration has not been assessed. Patients, methods: The study sample comprised 147 patients with DTC referred to our center between May 2008 and September 2010. All patients received TE with subsequent RRA. None of these 147 patients had evidence of distant metastasis. 93 patients had endogenous TSH stimulation 4–5 weeks after surgery (group I) and twenty-six received two rhTSH injections (group II). 28 patients were treated with a single rhTSH injection after a brief THW (group III). RRA-Efficacy was assessed three months after therapy by diagnostic whole-body scan and measurement of the tumour marker thyroglobulin (Tg) under TSH stimulation. Results: Three categories of success were defined for remnant ablation. Based on the definition of successful remnant ablation no visible uptake and a Tg ≤ 2.0 ng/ ml (category 1) was seen in 62/93 patients in group I, in 17/26 patients in group II (p = n.s.) and in 12/28 patients in group III (p < 0.05). Visible radioiodine uptake and a Tg ≤ 2.0 ng/ml (category 2) was seen in 16/28 patients of group III and thus significantly more frequent than in group I (28/93 patients) (p < 0.01). However, patients in group III (16/28 patients) and group II (8/26 patients) showed no significant difference in this category (p = n.s.). Visible radioiodine uptake and a Tg > 2.0 ng/ml (category 3) was found in 3/93 patients in group I and 1/26 patients in group II but in no patient in group III. Conclusion: The third strategy of remnant ablation using a single injection of rhTSH after a brief THW period resulted in a significant higher rate of patients with residual uptake in the thyroid bed and a Tg level below 2 ng/ml three months after remnant ablation in comparison to THW. However, the overall efficacy of the third protocol was not significantly different as compared to two rhTSH injections. Under the aspect of the supply shortage of rhTSH the combined endogenous and exogenous TSH stimulation may be an attractive alternative for remnant ablation in differentiated thyroid cancer.

Recombinant human thyrotropin preparation for adjuvant radioiodine treatment in children and adolescents with differentiated thyroid cancer

AIM

Although recombinant human thyrotropin (rhTSH) is widely used in treating differentiated thyroid cancer (DTC), almost all clinical investigation has been in adults. The aim of our retrospective study was to evaluate outcomes of adjuvant, rhTSH-aided radioiodine treatment in children/adolescents with DTC and to compare them to (131)I therapy during l-thyroxin withdrawal (THW).

METHODS

Patients with the diagnosis of DTC who were ≤18 years of age and had no signs of persistent disease at the time of (131)I treatment were included; 48 patients were treated after rhTSH (rhTSH group) and 82 after THW group. The median time of follow-up after therapy was 67 months and was longer in the THW group (99 vs 43 months, P<0.05).

RESULTS

On the day of (131)I administration, all but one patient had TSH levels above 25 μIU/ml. Peak TSH concentration was significantly higher in the rhTSH group (152 μIU/ml vs 91 μIU/ml). Similarly, the thyroglobulin concentration was higher in the rhTSH group (9.7 ng/ml vs 1.8 ng/ml). No side effects requiring medical intervention were recorded after rhTSH administration. The evaluation of disease outcomes during TSH stimulation (6-18 months after (131)I treatment) revealed equal rates of thyroid ablation (71%) in both groups. During subsequent follow-up, five patients showed recurrence (P>0.05).

CONCLUSIONS

In children/adolescents, rhTSH-aided adjuvant radioiodine treatment is associated with rates of remnant ablation and short-term recurrence similar to THW. As this preparation has several advantages over THW, rhTSH may become the preferred method of TSH stimulation once studies of long-term outcomes show non-inferiority to THW in this age group.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Outpatient thyroid remnant ablation using repeated low 131-iodine activities (740 MBq/20 mCix2) in patients with low-risk differentiated thyroid cancer

CONTEXT

In low-risk differentiated thyroid cancer (DTC), postoperative (131)I remnant ablation should employ a minimum effective activity; reports increasingly suggest efficacy of low activities, e.g. 1110 MBq/30 mCi. OBJECTIVES, DESIGN, PATIENTS, AND INTERVENTIONS: We retrospectively studied the ablation capability and diagnostic utility of the Minidose protocol, two 740-MBq/20 mCi outpatient administrations, 6-18 months apart, plus related diagnostic procedures, in 160 consecutive (near-) totally thyroidectomized low-risk DTC (pT1/N0-Nx) patients. Successful ablation comprised negative 740-MBq whole-body scintigraphy with cervical uptake below 0.1%, negative stimulated thyroglobulin (STg) (<1 ng/ml, negative thyroglobulin antibodies), and negative Doppler ultrasonography (performed around Minidose 2).

SETTING

The study took place at a referral center.

RESULTS

Minidose imaging found unsuspected nodal or distant metastases in nine of 160 patients (5.6%). Ablation success rates after one (two) 740-MBq activity (activites) were 75.9% (90.2%) in 145 (132) evaluable imaging-negative patients. Compared with thyroid hormone withdrawal, recombinant human TSH stimulation was associated with higher urinary iodine excretion/creatinine, lower cervical uptake, and more frequent ablation success after the first 740 MBq; success rates no longer differed significantly after both administrations. Patients with STg below 10 ng/ml at Minidose 1 were oftener ablated at Minidose 2 (odds ratio=13.9, 95% confidence interval=2.5-76.4, P<0.003), attaining 92.0% final ablation success after recombinant human TSH preparation, suggesting that one 740-MBq activity should suffice in this subgroup. All 81 evaluable patients with prolonged follow-up (mean 41.8±21.9 months after Minidose 1) had no evidence of disease at the last visit.

CONCLUSIONS

The Minidose outpatient ablation protocol is effective and diagnostically useful in low-risk DTC.

Radioiodine for remnant ablation and therapy of metastatic disease

Radioiodine is considered an effective and low-risk therapy modality of advanced differentiated thyroid cancer. For patients without lymph-node or distant metastases and low stages of the primary tumor, debate is ongoing about the necessity of thyroid remnant tissue ablation in an adjuvant setting. On the basis of evidence from retrospective studies, and until results of ongoing controlled prospective randomized trials become available, (131)I ablation of remnant thyroid tissue in patients with primary tumors >1 cm is advisable. For thyroid remnant ablation, individual dosimetry is not obligatory. By contrast, the effectiveness of (131)I therapy of locally advanced and/or metastatic disease can be improved by individual dosimetry. For practical reasons, an approach delivering the maximal possible radiation dose to the tumor without exceeding a critical blood dose of approximately 2 Gy seems advantageous. The availability of recombinant human TSH (rhTSH) has improved the quality of life of patients and reduces the radiation exposure of healthy nonthyroid tissue compared with TSH stimulation through levothyroxine withdrawal. In patients with distant metastases, rhTSH stimulation is possible only in off-label use, from which especially elderly and frail patients may benefit, as they most severely suffer from hypothyroidism caused by thyroid hormone withdrawal.

Radio-iodine therapy in differentiated thyroid cancer: indications and procedures

Post-surgical ablative iodine-131 therapy is recommended for all differentiated thyroid cancer primary tumors>1 cm in diameter. Regarding smaller primary tumors, 131I ablation may be helpful in special cases: tumor close to the thyroid capsule, previous percutaneous radiation to the neck, familial occurrence of thyroid cancer, tumor diameter 5-10 mm, and unfavorable histological variants. In this context, the patient's preferences for safety should be considered. In most centers, standard fixed activities of 1-3 GBq are used for 131I ablation. Preparation for the procedure with such activities requires a low-iodine diet for 2-3 weeks and stimulation of thyroid stimulating hormone (TSH) by withholding of thyroid hormone for 3 weeks following thyroidectomy or by use of recombinant human TSH. The advantages of recombinant TSH are avoidance of hypothyroid morbidity and consequently a better quality of life, as well as a lower radiation dose to extra-thyroidal compartments. To treat metastastic differentiated thyroid cancer, higher activities of radio-iodine (in the range 4-11 GBq) are necessary; if possible, individual dosimetry is recommended. The standard approach to preparation for 131I therapy in patients with metastases is endogenous hypothyroidism after thyroid hormone withdrawal.

Recombinant human thyroid-stimulating hormone is effective for radioiodine ablation of post-surgical thyroid remnants

OBJECTIVE

To investigate whether recombinant human thyroid-stimulating factor (rhTSH) is effective for the radiometabolic ablation of post-surgery thyroid remnants, using low doses of (131)I.

PATIENTS AND METHODS

The study included two groups of patients enrolled consecutively: group 1 consisted of 52 patients with papillary cancer or minimally invasive follicular cancer (stage I and II), and group 2 consisted of 41 patients with the same stage of disease. All patients underwent a total thyroidectomy. Group 1 received 1.11 GBq (30 mCi) (131)I for post-surgical remnants ablation with the aid of rhTSH, while group 2, in the hypothyroid state, received the same amount of radioiodine. To minimize iodine interference, all patients remained on a low iodine diet for 2 weeks and L-thyroxine (L-T4) was stopped for 4 days in the group of patients treated with the aid of rhTSH. To investigate (131)I uptake in this group, a tracer dose was administered 3 h after the second injection of rhTSH and the uptake was evaluated at 24 h just before administration of the therapeutic dose. I was also measured in the patients treated in the hypothyroid state just before the therapeutic dose was given.

RESULTS

After 1 year both groups were studied by using whole-body scintigraphy (WBS) and measuring thyroglobulin after rhTSH. In group 1, WBS was negative in 76.9% (40 patients), while thyroglobulin-stimulated levels were <1.0 ng . ml(-1) in 86.5% (45 patients). In Group 2, WBS was negative in 75.6% (31 patients), while thyroglobulin-stimulated levels were <1 ng . ml(-1) in 78.0% (32 patients). (131)I uptake was 2.29+/-0.45 in the group treated with the aid of rhTSH, and 3.30+/-0.7 in the group treated in the hypothyroid state (P=0.2). No patients treated with the aid of rhTSH and with the short stoppage of L-T4 experienced symptoms of hypothyroidism, and free thyroxine (FT4) and thyroid-stimulating hormone levels remained normal.

CONCLUSIONS

Our data confirm that, when the interference of iodine is minimized, rhTSH is highly effective for the treatment of post-surgical thyroid remnants using a low dose of (131)I.

Comparison of iodine uptake in tumour and nontumour tissue under thyroid hormone deprivation and with recombinant human thyrotropin in thyroid cancer patients

AIM

Recombinant human thyrotropin (rhTSH) is a new option for diagnostic follow-up in patients with differentiated thyroid cancer (DTC). Iodine kinetics after administration of rhTSH is controversially discussed. The aim of our study was to compare the time course of radioiodine in tumour and normal tissue during periods of TSH elevation in patients in a hypothyroid state (HS) following hormone withdrawal, with those under euthyroidism (ES) after the administration of rhTSH.

PATIENTS AND METHODS

We investigated four patients who had undergone near-total thyroidectomy and were suffering from metastatic disease. Dosimetric calculations were performed using tumour and whole-body uptake, and background measurements from 123-iodine scans performed 0, 4, 24 and 48 h after the application of (123)I.

RESULTS

All patients had lesser uptake of (123)I under rhTSH stimulation than after hormone withdrawal. The median maximum TG (thyroglobulin) levels were 733.1 ng/ml with HS and 548.0 ng/ml with ES. The median half-life in tumour tissue was 39.8 h (mean 65.9, range 11.5-194.0) with HS and 21.9 h (mean 38.7, range. 8.7-113.9) with ES. The median uptake dose in per cent in tumour tissue was 0.08 (mean 0.15, range 0.04-0.6) with HS and 0.05 (mean 0.08, range 0.03-0.2) with ES. Furthermore, the cumulative activity in metastatic tissue was lower after rhTSH than during hypothyroidism, with considerable variations between individual lesions.

CONCLUSION

In our small group of DTC patients with metastatic disease, the effectiveness of radioiodine therapy following rhTSH was anticipated to be less than that in individuals who were hypothyroid after levothyroxine (L-T(4)) withdrawal. Endogenous TSH stimulation of metastatic thyroid cancer with radioiodine should not be performed without prior target tumour lesion dosimetry with (123)I.