99mTc-MIBI Imaging in the presurgical characterization of thyroid follicular neoplasms: relationship to multidrug resistance protein expression.
Recently, thyroid (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) scintiscanning has been proposed in an attempt to preoperatively identify thyroid malignancies, but discrepant results have been reported for oncocytic lesions. The aim of this study was to investigate the usefulness of visual and semiquantitative analyses of (99m)Tc-MIBI scintigraphy for preoperatively characterizing thyroid nodules with indeterminate cytologic diagnoses, segregating in advance nononcocytic variants from those that are oncocytic. This study also aimed to analyze the relationship between (99m)Tc-MIBI images and P-glycoprotein (P-gp)/multidrug resistance-associated protein-1 (MRP1) immunohistochemical expression.


METHODS
Fifty-one consecutive patients with cold thyroid nodules cytologically diagnosed as nononcocytic or oncocytic follicular neoplasm were prospectively studied. Visual and semiquantitative (99m)Tc-MIBI scanning was performed and the diagnoses of the lesions were histologically proven by subsequent thyroidectomy. Immunohistochemical evaluation of P-gp and MRP1 was also performed on surgical samples.


RESULTS
Visual and semiquantitative (99m)Tc-MIBI scintiscans showed a low specificity in preoperatively discriminating malignant oncocytic lesions. In nononcocytic nodules, the semiquantitative method was more accurate than the visual (94.44% and 77.78%, respectively). P-gp protein expression was negative in all thyroid lesions, whereas apical plasma membrane MRP1 expression was found in 78% of the lesions with a negative (99m)Tc-MIBI retention index, compared with 11% of lesions with a positive retention index, correlating most strongly with a negative (99m)Tc-MIBI RI in those cases with strong MRP1 apical expression.


CONCLUSIONS
Semiquantitative (99m)Tc-MIBI scintigraphy is an adjunctive method to predict preoperatively the malignant behavior of nononcocytic follicular thyroid nodules indeterminate at fine-needle aspiration biopsy, with a potential impact on the definition of their clinical management. Moreover, the good correlation found between immunohistochemical apical expression of MRP1 and the scintigraphic findings supports the (99m)Tc-MIBI results and provides tissue information on the molecular mechanisms responsible for (99m)Tc-MIBI images in thyroid lesions.
Saggiorato
Enrico
E
Section of Endocrinology, Division of Internal Medicine, Department of Clinical and Biological Sciences, Gradenigo Hospital, University of Turin, Turin, Italy. enrico.saggiorato@unito.it
Angusti
Tiziana
T
Rosas
Rosy
R
Martinese
Morena
M
Finessi
Monica
M
Arecco
Federico
F
Trevisiol
Edoardo
E
Bergero
Nicoletta
N
Puligheddu
Barbara
B
Volante
Marco
M
Podio
Valerio
V
Papotti
Mauro
M
Orlandi
Fabio
F
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D011877:Radionuclide Imaging; D017256:Technetium Tc 99m Sestamibi; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000235:genetics* / Q000473:pathology / Q000601:surgery; D016606:Thyroid Nodule / Q000000981:diagnostic imaging / Q000235:genetics / Q000473:pathology / Q000601:surgery
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D017256:Technetium Tc 99m Sestamibi; C421109:multidrug resistance-associated protein 1