CLINICAL UTILITY OF A SECOND RECOMBINANT HUMAN TSH STIMULATION IN DIFFERENTIATED THYROID CANCER PATIENT

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Torlontano M.1, Crocetti U.1, Durante C.4, Attard M.5, Maniglia A.5, Tumino S.6, Bruno R.7, Bonfitto N.2, Dicembrino F.3, Varraso A.3, Meringolo D.8, Filetti S.4, Trischitta V.1,4,9
1Units of Endocrinology, 2Thoracic Surgery, 3Nuclear Medicine, Scientific Institute Casa Sollievo della Sofferenza, S. Giovanni Rotondo, Italy, 4Department of Clinical Sciences, Sapienza University, Rome, Italy, 5Unit of Endocrinology, Cervello Hospital, Palermo, Italy, 6Department of Biomedical Sciences, University of Catania, Catania, Italy, 7Unit of Endocrinology, Tinchi-Pisticci Hospital, Matera, Italy, 8Unit of Endocrinology, Bentivoglio Hospital, Bologna, Italy, 9Casa Sollievo della Sofferenza-Mendel Institute, Rome, Italy

Abstract

Serum thyroglobulin (Tg) level after recombinant human TSH (rhTSH) stimulation and neck ultrasonography (US) are important tools in the first follow-up of differentiated thyroid cancer (DTC) patients.
Objectives: to investigate if a second rhTSH stimulation, performed 2-3 years later, is of clinical utility in the follow-up of these patients.
Patients and Methods: 101 consecutive DTC patients (76 females, 25 males, mean age 40.3±11.5 years, ranging 14-69) were studied. They had been treated by surgery and radioiodine ablation and exhibited, at first rhTSH, either undetectable (?1 ng/ml) (rhTSH1-Tg-, n= 89 pts) or low (>1-5 ng/ml) (rhTSH1-Tg+, n= 12 pts) Tg, without US evidence of residual disease. Inclusion criteria were well differentiated DTC, complete surgery, no pathological uptake at post-ablation whole body 131I-scintigraphy and absence of Tg-antibodies.
Results: at second rhTSH stimulation, all 89 rhTSH1-Tg- patients exhibited negative US and only one subject became Tg+ (2.2 ng/ml); although this patient showed also negative CT scan, she was considered as uncertain. Thus, negative predictive value of the combination of rhTSH1-Tg- plus negative US at first follow-up was 98.5% (88/89 patients). RhTSH2-Tg became undetectable in 6 out the 12 rhTSH1-Tg+ patients, resembling previous data obtained after thyroid hormone withdrawal, while 2 out the remaining 6 patients showed disease persistence/recurrence (neck lymph nodes), with a positive predictive value of rhTSH1-Tg+ of 16.7% (2/12 patients).
Conclusions: a second stimulation is useless in patients previously rhTSH-Tg and US negative, but indicated in those with low-detectable rhTSH-Tg levels at first follow-up. Since many rhTSH1-Tg+ patients become spontaneously Tg- at second stimulation, we suggest that a low-positive rhTSH1-Tg plus negative imaging does not necessarily imply the presence of disease persistence; consequently, in the absence of clinical or US evidence of disease persistence, these patients should not be re-treated by radioiodine but simply scheduled to a later rhTSH stimulation.