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

Summary

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.

Zusammenfassung

Ziel: Die Radioiodtherapie (RIT) nach primär kompletter bzw. fast kompletter Thyreoid - ektomie ist ein Hauptbestandteil bei nahezu allen differenzierten Schilddrüsenkarzinomen (Differentiated Thyroid Cancer; DTC). Verglichen mit der konventionellen endogenen Stimulation zeigt die exogene Stimulation mit rhTSH vor RIT vergleichbare Ergebnisse: Ein weiterer möglicher Ansatz der TSH-Stimulation ist ein kurzer Hormonentzug mit anschließender einmaliger rhTSH-Injektion. Bisher wurde die Wirksamkeit der RIT nach diesem Schema nicht untersucht. Patienten, Methoden: Die retrospektive Analyse umfasste 147 Patienten mit DTC, die in der Klinik und Poliklinik für Nuklearmedizin des Universitätsklinikum Münster zwischen Mai 2008 und September 2010 behandelt wurden. Alle Patienten erhielten eine komplette bzw. fast komplette Thyreoidektomie mit anschließender RIT. Keiner dieser 147 Patienten hatte Hinweise auf Fernmetastasen. Bei 93 Patienten erfolgte eine endogene TSH-Stimulation für vier bis fünf Wochen nach der Operation (Gruppe I) und 26 Patienten erhielten eine exogene TSH-Stimulation mit zwei rhTSH Injektionen (Gruppe II). 28 Patienten wurden nach 14-tägigem Hormonentzug zur zusätzlichen TSHStimulation mit einer einzigen rhTSH-Injektion vorbereitet (Gruppe III). Die Wirksamkeit der RIT wurde drei Monate nach der Therapie mit diagnostischer 131I-Ganzkörperszintigraphie und Bestimmung des Tumormarker Thyreoglobulin (Tg) unter TSH-Stimulation kontrolliert. Ergebnisse: Zur Beurteilung des Therapieerfolgs wurden die Patienten drei Kategorien zugeordnet. Keine sichtbare zervikale Radioiodanreicherung und ein Tg ≤ 2,0 ng/ml (Kategorie 1) fanden sich bei 62/93 Patienten der Gruppe I, 17/26 Patienten der Gruppe II (p = n.s.) und 12/28 der Gruppe III (p < 0.05). Eine sichtbare Anreicherung und ein Tg ≤ 2,0 ng/ml (Kategorie 2) zeigten sich bei 16/28 Patienten der Gruppe III und damit signifikant häufiger als in Gruppe I (28/93 Patienten) (p < 0,01). Demgegenüber ließ sich in dieser Kate-gorie kein signifikanter Unterschied zwischen Patienten der Gruppe III (16/28 Patienten) und Gruppe II (8/26 Patienten) nachweisen (p = n.s.). Ein sichtbarer Radioiod-Uptake und ein Tg > 2,0 ng/ml (Kategorie 3) traten bei 3/93 Patienten der Gruppe I und 1/26 Patienten der Gruppe II, jedoch bei keinem Patienten der Gruppe III auf. Schlussfolgerung: Im Vergleich zur endogenen TSH-Stimulation führte die Kombination aus endogener und exogener TSH-Stimulation drei Monate nach der Restgewebeablation zu einer signifikant höheren Rate von Patienten mit residualem Uptake im Schilddrüsenlager bei einem Tg < 2 ng/ml. Demgegenüber unterschied sich die Effektivität der Restgewebeablation nach einer einzelnen Injektion von rhTSH und einem kurzen Absetzen der Schilddrüsenhormone nicht von derjenigen nach exogener TSH-Stimulation nach zwei rhTSH-Injektionen. Unter Berücksichtigung des Lieferengpasses von rhTSH kann die Kombination aus endo- und exogener TSHStimulation eine attraktive Alternative der Restgewebeablation bei Patienten mit differenzierten Schilddrüsenkarzinomen sein.

Keywords

Radioiodine - remnant ablation - thyroid hormone withdrawal - rhTSH

Schlüsselwörter

Radioiod - Restgewebeablation - Schilddrüsenhormonentzug - rhTSH

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