Chromosome translocation frequency after radioiodine thyroid remnant ablation: a comparison between recombinant human thyrotropin stimulation and prolonged levothyroxine withdrawal.
BACKGROUND
Thyroid remnant ablation of differentiated thyroid carcinoma (DTC) patients is traditionally performed after levothyroxine withdrawal. Recombinant human TSH (rhTSH) administration increases serum TSH levels without inducing hypothyroidism.


OBJECTIVE
The aim of the study was to investigate the frequency of chromosome translocations in DTC patients after the first (131)I therapeutic dose and compare the frequency of translocations between DTC patients off levothyroxine and those receiving rhTSH.


METHODS
A total of 20 DTC patients were randomly assigned to levothyroxine withdrawal [(30 d) group A; n=10, nine women; mean age 48.5+/- 19.2 yr] or rhTSH injections [(0.9 mg im per 2 consecutive days) group B; n=10, eight women; mean age 50.4+/- 18.8 yr] before undergoing (131)I activity (3.7 GBq). The frequency of translocations in peripheral lymphocytes was analyzed by tricolor fluorescence in situ hybridization with whole-chromosome-specific probes for chromosomes 1, 4, and 8. Lymphocytes were stained routinely (about 500 each time).


RESULTS
The two groups showed similar baseline translocation frequency. After (131)I administration, the total chromosomal translocation rate was significantly lower in group B than group A (P = 0.02). The frequency of translocations increased significantly in group A only (P = 0.01 vs. baseline). Rearrangement specifically involved chromosomes 4 and 8 (P = 0.02 vs. baseline).


CONCLUSIONS
Our preliminary data show that in hypothyroid status (131)I ablation therapy induces a higher translocation rate, especially in chromosomes 4 and 8. This finding, in agreement with previous dosimetric reports, suggests that whereas inducing a low extrathyroid exposure, rhTSH reduces the potential risk of chromosomal aberration associated with blood irradiation.
Frigo
Anna
A
Department of Surgical and Biomedical Sciences, University of Verona, 37129 Verona, Italy.
Dardano
Angela
A
Danese
Elisa
E
Davì
Maria Vittoria
MV
Moghetti
Paolo
P
Colato
Chiara
C
Francia
Giuseppe
G
Bernardi
Franca
F
Traino
Claudio
C
Monzani
Fabio
F
Ferdeghini
Marco
M
D000328:Adult; D000368:Aged; D001853:Bone Marrow / Q000528:radiation effects; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins / Q000627:therapeutic use; D013964:Thyroid Neoplasms / Q000235:genetics / Q000532:radiotherapy*; D013972:Thyrotropin / Q000627:therapeutic use*; D013974:Thyroxine / Q000008:administration & dosage*; D014178:Translocation, Genetic
D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D013972:Thyrotropin; D013974:Thyroxine